javascript double ampersand assignment

Home » JavaScript Tutorial » An Introduction to JavaScript Logical Operators

An Introduction to JavaScript Logical Operators

Summary : in this tutorial, you will learn how to use the JavaScript logical operators including the logical NOT operator( ! ), the logical AND operator ( && ) and the logical OR operator ( || ).

The logical operators are important in JavaScript because they allow you to compare variables and do something based on the result of that comparison.

For example, if the result of the comparison is true , you can run a block of code; if it’s false , you can execute another code block.

JavaScript provides three logical operators:

• ! (Logical NOT)
• || (Logical OR)
• && (Logical AND)

1) The Logical NOT operator (!)

JavaScript uses an exclamation point ! to represent the logical NOT operator. The ! operator can be applied to a single value of any type, not just a Boolean value.

When you apply the ! operator to a boolean value, the ! returns true if the value is false and vice versa. For example:

In this example, the eligible is true so !eligible returns false . And since the required is true , the !required returns false .

When you apply the ! operator to a non-Boolean value. The ! operator converts the value to a boolean value and then negates it.

The following example shows how to use the ! operator:

The logical ! operator works based on the following rules:

• If a is undefined , the result is true .
• If a is null , the result is true .
• If a is a number other than 0 , the result is false .
• If a is NaN , the result is true .
• If a is an object , the result is false.
• If a is an empty string, the result is true . If a is a non-empty string, the result is false

The following demonstrates the results of the logical ! operator when applying to a non-boolean value:

Double-negation ( !! )

Sometimes, you may see the double negation ( !! ) in the code. The !! uses the logical NOT operator ( ! ) twice to convert a value to its real boolean value.

The result is the same as using the Boolean() function. For example:

The first ! operator negates the Boolean value of the counter variable. If the counter is true , then the ! operator makes it false and vice versa.

The second ! operator negates the result of the first ! operator and returns the real boolean value of the counter variable.

2) The Logical AND operator (&&)

JavaScript uses the double ampersand ( && ) to represent the logical AND operator. The following expression uses the && operator:

If a can be converted to true , the && operator returns the b ; otherwise, it returns the a . This rule is applied to all boolean values.

The following truth table illustrates the result of the && operator when it is applied to two Boolean values:

The result of the && operator is true only if both values are true , otherwise, it is false . For example:

In this example, the eligible is false , therefore, the value of the expression eligible && required is false .

See the following example:

In this example, both eligible and required are true , therefore, the value of the expression eligible && required is true .

Short-circuit evaluation

The && operator is short-circuited. It means that the && operator evaluates the second value only if the first one doesn’t suffice to determine the value of an expression. For example:

In this example, b is true therefore the && operator could not determine the result without further evaluating the second expression ( 1/0 ).

The result is Infinity which is the result of the expression ( 1/0 ). However:

In this case, b is false , the && operator doesn’t need to evaluate the second expression because it can determine the final result as false based value of the first value.

The chain of && operators

The following expression uses multiple && operators:

The &&  operator carries the following:

• Evaluates values from left to right.
• For each value, convert it to a boolean. If the result is  false , stops and returns the original value.
• If all values are truthy values, return the last value.

In other words, The && operator returns the first falsey value or the last truthy value.

If a value can be converted to  true , it is called a truthy value. If a value can be converted to  false , it is a called a falsey value.

3) The Logical OR operator (||)

JavaScript uses the double-pipe || to represent the logical OR operator. You can apply the || operator to two values of any type:

If  a can be converted to  true , returns  a ; else, returns  b . This rule is also applied to boolean values.

The following truth table illustrates the result of the || operator based on the value of the operands:

The || operator returns false if both values are evaluated to false . In case either value is true , the || operator returns true . For example:

See another example:

In this example, the expression eligible || required returns false because both values are false .

The || operator is also short-circuited

Similar to the && operator, the || operator is short-circuited. It means that if the first value evaluates to true , the && operator doesn’t evaluate the second one.

The chain of || operators

The following example shows how to use multiple || operators in an expression:

The ||  operator does the following:

• For each value, convert it to a boolean value. If the result of the conversion is  true , stops and returns the value.
• If all values have been evaluated to false , returns the last value.

In other words, the chain of the ||  operators returns the first truthy value or the last one if no truthy value is found.

Logical operators

There are four logical operators in JavaScript: || (OR), && (AND), ! (NOT), ?? (Nullish Coalescing). Here we cover the first three, the ?? operator is in the next article.

Although they are called “logical”, they can be applied to values of any type, not only boolean. Their result can also be of any type.

Let’s see the details.

The “OR” operator is represented with two vertical line symbols:

In classical programming, the logical OR is meant to manipulate boolean values only. If any of its arguments are true , it returns true , otherwise it returns false .

In JavaScript, the operator is a little bit trickier and more powerful. But first, let’s see what happens with boolean values.

There are four possible logical combinations:

As we can see, the result is always true except for the case when both operands are false .

If an operand is not a boolean, it’s converted to a boolean for the evaluation.

For instance, the number 1 is treated as true , the number 0 as false :

Most of the time, OR || is used in an if statement to test if any of the given conditions is true .

For example:

We can pass more conditions:

OR "||" finds the first truthy value

The logic described above is somewhat classical. Now, let’s bring in the “extra” features of JavaScript.

The extended algorithm works as follows.

Given multiple OR’ed values:

The OR || operator does the following:

• Evaluates operands from left to right.
• For each operand, converts it to boolean. If the result is true , stops and returns the original value of that operand.
• If all operands have been evaluated (i.e. all were false ), returns the last operand.

A value is returned in its original form, without the conversion.

In other words, a chain of OR || returns the first truthy value or the last one if no truthy value is found.

For instance:

This leads to some interesting usage compared to a “pure, classical, boolean-only OR”.

Getting the first truthy value from a list of variables or expressions.

For instance, we have firstName , lastName and nickName variables, all optional (i.e. can be undefined or have falsy values).

Let’s use OR || to choose the one that has the data and show it (or "Anonymous" if nothing set):

If all variables were falsy, "Anonymous" would show up.

Short-circuit evaluation.

Another feature of OR || operator is the so-called “short-circuit” evaluation.

It means that || processes its arguments until the first truthy value is reached, and then the value is returned immediately, without even touching the other argument.

The importance of this feature becomes obvious if an operand isn’t just a value, but an expression with a side effect, such as a variable assignment or a function call.

In the example below, only the second message is printed:

In the first line, the OR || operator stops the evaluation immediately upon seeing true , so the alert isn’t run.

Sometimes, people use this feature to execute commands only if the condition on the left part is falsy.

&& (AND)

The AND operator is represented with two ampersands && :

In classical programming, AND returns true if both operands are truthy and false otherwise:

An example with if :

Just as with OR, any value is allowed as an operand of AND:

AND “&&” finds the first falsy value

Given multiple AND’ed values:

The AND && operator does the following:

• For each operand, converts it to a boolean. If the result is false , stops and returns the original value of that operand.
• If all operands have been evaluated (i.e. all were truthy), returns the last operand.

In other words, AND returns the first falsy value or the last value if none were found.

The rules above are similar to OR. The difference is that AND returns the first falsy value while OR returns the first truthy one.

We can also pass several values in a row. See how the first falsy one is returned:

When all values are truthy, the last value is returned:

The precedence of AND && operator is higher than OR || .

So the code a && b || c && d is essentially the same as if the && expressions were in parentheses: (a && b) || (c && d) .

Sometimes, people use the AND && operator as a "shorter way to write if ".

The action in the right part of && would execute only if the evaluation reaches it. That is, only if (x > 0) is true.

So we basically have an analogue for:

Although, the variant with && appears shorter, if is more obvious and tends to be a little bit more readable. So we recommend using every construct for its purpose: use if if we want if and use && if we want AND.

The boolean NOT operator is represented with an exclamation sign ! .

The syntax is pretty simple:

The operator accepts a single argument and does the following:

• Converts the operand to boolean type: true/false .
• Returns the inverse value.

A double NOT !! is sometimes used for converting a value to boolean type:

That is, the first NOT converts the value to boolean and returns the inverse, and the second NOT inverses it again. In the end, we have a plain value-to-boolean conversion.

There’s a little more verbose way to do the same thing – a built-in Boolean function:

The precedence of NOT ! is the highest of all logical operators, so it always executes first, before && or || .

What's the result of OR?

What is the code below going to output?

The answer is 2 , that’s the first truthy value.

What's the result of OR'ed alerts?

What will the code below output?

The answer: first 1 , then 2 .

The call to alert does not return a value. Or, in other words, it returns undefined .

• The first OR || evaluates its left operand alert(1) . That shows the first message with 1 .
• The alert returns undefined , so OR goes on to the second operand searching for a truthy value.
• The second operand 2 is truthy, so the execution is halted, 2 is returned and then shown by the outer alert.

There will be no 3 , because the evaluation does not reach alert(3) .

What is the result of AND?

What is this code going to show?

The answer: null , because it’s the first falsy value from the list.

What is the result of AND'ed alerts?

What will this code show?

The answer: 1 , and then undefined .

The call to alert returns undefined (it just shows a message, so there’s no meaningful return).

Because of that, && evaluates the left operand (outputs 1 ), and immediately stops, because undefined is a falsy value. And && looks for a falsy value and returns it, so it’s done.

The result of OR AND OR

What will the result be?

The answer: 3 .

The precedence of AND && is higher than || , so it executes first.

The result of 2 && 3 = 3 , so the expression becomes:

Now the result is the first truthy value: 3 .

Check the range between

Write an if condition to check that age is between 14 and 90 inclusively.

“Inclusively” means that age can reach the edges 14 or 90 .

Check the range outside

Write an if condition to check that age is NOT between 14 and 90 inclusively.

Create two variants: the first one using NOT ! , the second one – without it.

The first variant:

The second variant:

A question about "if"

Which of these alert s are going to execute?

What will the results of the expressions be inside if(...) ?

The answer: the first and the third will execute.

Check the login

Write the code which asks for a login with prompt .

If the visitor enters "Admin" , then prompt for a password, if the input is an empty line or Esc – show “Canceled”, if it’s another string – then show “I don’t know you”.

The password is checked as follows:

• If it equals “TheMaster”, then show “Welcome!”,
• Another string – show “Wrong password”,
• For an empty string or cancelled input, show “Canceled”

The schema:

Please use nested if blocks. Mind the overall readability of the code.

Hint: passing an empty input to a prompt returns an empty string '' . Pressing ESC during a prompt returns null .

Run the demo

Note the vertical indents inside the if blocks. They are technically not required, but make the code more readable.

Lesson navigation

• © 2007—2024  Ilya Kantor
• about the project
• terms of usage
• privacy policy

DEV Community

Posted on Nov 9, 2021 • Updated on Nov 29, 2021

Importance of double ampersand: logical AND(&&)in JavaScript

• Saves time and code length.
• Gets rid of else statement. Basic Example: > if/else statement let x= 2, y =5; if(y>x){ console.log("y is greater than x"); return; }

Using logical AND (&&) as short-circuit property let x= 2, y =5; y>x && console.log("y is greater than x");

• The difference the Short-Circuit property makes that you are able to write the code in few lines and is considered as one of the important features of JavaScript and hence making the JavaScript so powerful.

Top comments (0)

Templates let you quickly answer FAQs or store snippets for re-use.

Are you sure you want to hide this comment? It will become hidden in your post, but will still be visible via the comment's permalink .

Hide child comments as well

For further actions, you may consider blocking this person and/or reporting abuse

Understanding JavaScript Promises

Rahul Vijayvergiya - Jul 29

The Journey of Building Gidalo: A Real Estate Marketing Platform

Frederick Aleoke-Malachi - Jul 24

Quick Guide: Resolving "Cannot find module 'ajv/dist/compile/codegen'" in React

Vuyokazi Mkane - Jul 24

TypeScript Stage 3 Decorators: A Journey Through Setup and Usage

Brian Baliach - Jul 24

We're a place where coders share, stay up-to-date and grow their careers.

Double && (and) Double || (or) = Double Functionality

Social Share Links

The and (&&) and or (||) operators in javascript do not function like traditional logical operators. We can use them to our advantage to eliminate some boilerplate code when writing conditional expressions.

Additional jsbin: https://jsbin.com/qipina/edit?js,output

[00:00] The double ampersand and double pipe are logical operators in JavaScript, but we can do some pretty cool shorthand conditional operations with them.

"[00:11] What's more fun -- Programming or Testing? Testing or Programming?" If I asked you if those two questions would have the same result, one would typically say yes, but in JavaScript, they will have two different answers because the order in which you ask the question has an impact.

[00:29] I'm asking one of the questions here, "Testing or Programming?" Right now, we're seeing that the result is "Testing," but if we were to change the order in which the question is asked, our result is going to change, even though we were using the same values to ask the question.

[00:48] The OR operator in JavaScript is checking if the value on the left-hand side is truthy. If it is, it returns the value from the left-hand side instead of simply giving you a Boolean equal to true.

[01:02] That means we're getting the entire programming object that we declared up here set as our result. Later, down here, in our render function, when we're accessing that result, we can pull the name property off of the programming object.

[01:17] Let's look at what happens if we put non-truthy values in here, like null or undefined. In both cases, we saw that our output updated to show "Testing." With the OR operator, if the left-hand side is undefined, it will return the entire value of the right-hand side.

[01:39] The AND operator is similar in that it can return one of the values being compared instead of a Boolean type. The differences are that it can only return the value on the right-hand side of the comparison and only if both the left and right-hand sides are truthy values.

[01:58] If we change this to null, we have no output because the left-hand side was not truthy, but when the value of both sides is truthy, we're getting the value of the right-hand side in our result, as we can see in our output.

[02:14] I want to show you how we can leverage these operators to do some more complex expressions. Here we have a list of activities. The main three in question here are three activities that are tied with a FunScore of 10.

[02:29] The first thing we're going to check is if our activity is "Board Games." If so, it wins, and it returns ActivityOne as our result. If it's false, then the OR kicks in, and it's going to continue looking for a truthy value.

[02:44] The next thing we're going to look for is "Teaching" in the ActivityTwo slot, and then for "Programming" in the ActivityTwo slot. If none of those evaluated to truthy, we're just going to compare the FunScore. If ActivityOne has a higher FunScore, we'll give that back. Lastly, we'll fall through to returning ActivityTwo.

[03:06] This is a useful tool because we can combine the "return right-hand side when all truthy" behavior of the AND operator with the "return the first truthy value we find" behavior of the OR operator to do some concise logical evaluations.

Member comments are a way for members to communicate, interact, and ask questions about a lesson.

The instructor or someone from the community might respond to your question Here are a few basic guidelines to commenting on egghead.io

Be on-Topic

Comments are for discussing a lesson. If you're having a general issue with the website functionality, please contact us at [email protected].

Avoid meta-discussion

• This was great!
• This was horrible!
• I didn't like this because it didn't match my skill level.
• +1 It will likely be deleted as spam.

Code Problems?

Should be accompanied by code! Codesandbox or Stackblitz provide a way to share code and discuss it in context

Details and Context

Vague question? Vague answer. Any details and context you can provide will lure more interesting answers!

• Skip to main content

• Logical AND assignment (&&=)

The logical AND assignment ( x &&= y ) operator only assigns if x is truthy .

Description

Short-circuit evaluation.

The logical AND operator is evaluated left to right, it is tested for possible short-circuit evaluation using the following rule:

(some falsy expression) && expr is short-circuit evaluated to the falsy expression;

Short circuit means that the expr part above is not evaluated , hence any side effects of doing so do not take effect (e.g., if expr is a function call, the calling never takes place).

Logical AND assignment short-circuits as well meaning that x &&= y is equivalent to:

And not equivalent to the following which would always perform an assignment:

Using logical AND assignment

Specifications.

Browser compatibility

• Logical AND (&&)
• The nullish coalescing operator ( ?? )
• Bitwise AND assignment ( &= )
• JavaScript basics
• JavaScript first steps
• JavaScript building blocks
• Introducing JavaScript objects
• Introduction
• Grammar and types
• Control flow and error handling
• Loops and iteration
• Expressions and operators
• Numbers and dates
• Text formatting
• Regular expressions
• Indexed collections
• Keyed collections
• Working with objects
• Details of the object model
• Using promises
• Iterators and generators
• Meta programming
• JavaScript modules
• Client-side JavaScript frameworks
• Client-side web APIs
• A re-introduction to JavaScript
• JavaScript data structures
• Equality comparisons and sameness
• Inheritance and the prototype chain
• Strict mode
• JavaScript typed arrays
• Memory Management
• Concurrency model and Event Loop
• References:
• AggregateError
• ArrayBuffer
• AsyncFunction
• BigInt64Array
• BigUint64Array
• FinalizationRegistry
• Float32Array
• Float64Array
• GeneratorFunction
• InternalError
• ReferenceError
• SharedArrayBuffer
• SyntaxError
• Uint16Array
• Uint32Array
• Uint8ClampedArray
• WebAssembly
• decodeURI()
• decodeURIComponent()
• encodeURI()
• encodeURIComponent()
• parseFloat()
• Addition (+)
• Addition assignment (+=)
• Assignment (=)
• Bitwise AND (&)
• Bitwise AND assignment (&=)
• Bitwise NOT (~)
• Bitwise OR (|)
• Bitwise OR assignment (|=)
• Bitwise XOR (^)
• Bitwise XOR assignment (^=)
• Comma operator (,)
• Conditional (ternary) operator
• Decrement (--)
• Destructuring assignment
• Division (/)
• Division assignment (/=)
• Equality (==)
• Exponentiation (**)
• Exponentiation assignment (**=)
• Function expression
• Greater than (>)
• Greater than or equal (>=)
• Grouping operator ( )
• Increment (++)
• Inequality (!=)
• Left shift (<<)
• Left shift assignment (<<=)
• Less than (<)
• Less than or equal (<=)
• Logical NOT (!)
• Logical OR (||)
• Logical OR assignment (||=)
• Logical nullish assignment (??=)
• Multiplication (*)
• Multiplication assignment (*=)
• Nullish coalescing operator (??)
• Object initializer
• Operator precedence
• Optional chaining (?.)
• Pipeline operator (|>)
• Property accessors
• Remainder (%)
• Remainder assignment (%=)
• Right shift (>>)
• Right shift assignment (>>=)
• Spread syntax (...)
• Strict equality (===)
• Strict inequality (!==)
• Subtraction (-)
• Subtraction assignment (-=)
• Unary negation (-)
• Unary plus (+)
• Unsigned right shift (>>>)
• Unsigned right shift assignment (>>>=)
• async function expression
• class expression
• delete operator
• function* expression
• in operator
• new operator
• void operator
• async function
• for await...of
• function declaration
• import.meta
• try...catch
• Arrow function expressions
• Default parameters
• Method definitions
• Rest parameters
• The arguments object
• Private class fields
• Public class fields
• constructor
• Error: Permission denied to access property "x"
• InternalError: too much recursion
• RangeError: argument is not a valid code point
• RangeError: invalid array length
• RangeError: invalid date
• RangeError: precision is out of range
• RangeError: radix must be an integer
• RangeError: repeat count must be less than infinity
• RangeError: repeat count must be non-negative
• ReferenceError: "x" is not defined
• ReferenceError: assignment to undeclared variable "x"
• ReferenceError: can't access lexical declaration "x" before initialization
• ReferenceError: deprecated caller or arguments usage
• ReferenceError: invalid assignment left-hand side
• ReferenceError: reference to undefined property "x"
• SyntaxError: "0"-prefixed octal literals and octal escape seq. are deprecated
• SyntaxError: "use strict" not allowed in function with non-simple parameters
• SyntaxError: "x" is a reserved identifier
• SyntaxError: JSON.parse: bad parsing
• SyntaxError: Malformed formal parameter
• SyntaxError: Unexpected token
• SyntaxError: Using //@ to indicate sourceURL pragmas is deprecated. Use //# instead
• SyntaxError: a declaration in the head of a for-of loop can't have an initializer
• SyntaxError: applying the "delete" operator to an unqualified name is deprecated
• SyntaxError: for-in loop head declarations may not have initializers
• SyntaxError: function statement requires a name
• SyntaxError: identifier starts immediately after numeric literal
• SyntaxError: illegal character
• SyntaxError: invalid regular expression flag "x"
• SyntaxError: missing ) after argument list
• SyntaxError: missing ) after condition
• SyntaxError: missing : after property id
• SyntaxError: missing ; before statement
• SyntaxError: missing = in const declaration
• SyntaxError: missing ] after element list
• SyntaxError: missing formal parameter
• SyntaxError: missing name after . operator
• SyntaxError: missing variable name
• SyntaxError: missing } after function body
• SyntaxError: missing } after property list
• SyntaxError: redeclaration of formal parameter "x"
• SyntaxError: return not in function
• SyntaxError: test for equality (==) mistyped as assignment (=)?
• SyntaxError: unterminated string literal
• TypeError: "x" has no properties
• TypeError: "x" is (not) "y"
• TypeError: "x" is not a constructor
• TypeError: "x" is not a function
• TypeError: "x" is not a non-null object
• TypeError: "x" is read-only
• TypeError: "x" is not iterable
• TypeError: More arguments needed
• TypeError: Reduce of empty array with no initial value
• TypeError: X.prototype.y called on incompatible type
• TypeError: can't access dead object
• TypeError: can't access property "x" of "y"
• TypeError: can't assign to property "x" on "y": not an object
• TypeError: can't define property "x": "obj" is not extensible
• TypeError: can't delete non-configurable array element
• TypeError: can't redefine non-configurable property "x"
• TypeError: cannot use "in" operator to search for "x" in "y"
• TypeError: cyclic object value
• TypeError: invalid "instanceof" operand "x"
• TypeError: invalid Array.prototype.sort argument
• TypeError: invalid arguments
• TypeError: invalid assignment to const "x"
• TypeError: property "x" is non-configurable and can't be deleted
• TypeError: setting getter-only property "x"
• TypeError: variable "x" redeclares argument
• URIError: malformed URI sequence
• Warning: -file- is being assigned a //# sourceMappingURL, but already has one
• Warning: 08/09 is not a legal ECMA-262 octal constant
• Warning: Date.prototype.toLocaleFormat is deprecated
• Warning: JavaScript 1.6's for-each-in loops are deprecated
• Warning: String.x is deprecated; use String.prototype.x instead
• Warning: expression closures are deprecated
• Warning: unreachable code after return statement
• JavaScript technologies overview
• Lexical grammar
• Enumerability and ownership of properties
• Iteration protocols
• Transitioning to strict mode
• Template literals
• Deprecated features

• DSA with JS - Self Paced
• JS Tutorial
• JS Exercise
• JS Interview Questions
• JS Operator
• JS Projects
• JS Examples
• JS Free JS Course
• JS A to Z Guide
• JS Formatter
• Explore GfG Premium

JS Arithmetic Operators

• Addition(+) Arithmetic Operator in JavaScript
• Subtraction(-) Arithmetic Operator in JavaScript
• Multiplication(*) Arithmetic Operator in JavaScript
• Division(/) Arithmetic Operator in JavaScript
• Modulus(%) Arithmetic Operator in JavaScript
• Exponentiation(**) Arithmetic Operator in JavaScript
• Increment(+ +) Arithmetic Operator in JavaScript
• Decrement(--) Arithmetic Operator in JavaScript
• JavaScript Arithmetic Unary Plus(+) Operator
• JavaScript Arithmetic Unary Negation(-) Operator

JS Assignment Operators

• Addition Assignment (+=) Operator in Javascript
• Subtraction Assignment( -=) Operator in Javascript
• Multiplication Assignment(*=) Operator in JavaScript
• Division Assignment(/=) Operator in JavaScript
• JavaScript Remainder Assignment(%=) Operator
• Exponentiation Assignment(**=) Operator in JavaScript
• Left Shift Assignment (<<=) Operator in JavaScript
• Right Shift Assignment(>>=) Operator in JavaScript
• Bitwise AND Assignment (&=) Operator in JavaScript
• Bitwise OR Assignment (|=) Operator in JavaScript
• Bitwise XOR Assignment (^=) Operator in JavaScript
• JavaScript Logical AND assignment (&&=) Operator
• JavaScript Logical OR assignment (||=) Operator
• Nullish Coalescing Assignment (??=) Operator in JavaScript

JS Comparison Operators

• Equality(==) Comparison Operator in JavaScript
• Inequality(!=) Comparison Operator in JavaScript
• Strict Equality(===) Comparison Operator in JavaScript
• Strict Inequality(!==) Comparison Operator in JavaScript
• Greater than(>) Comparison Operator in JavaScript
• Greater Than or Equal(>=) Comparison Operator in JavaScript
• Less Than or Equal(

JS Logical Operators

• NOT(!) Logical Operator inJavaScript
• AND(&&) Logical Operator in JavaScript
• OR(||) Logical Operator in JavaScript

JS Bitwise Operators

• AND(&) Bitwise Operator in JavaScript
• OR(|) Bitwise Operator in JavaScript
• XOR(^) Bitwise Operator in JavaScript
• NOT(~) Bitwise Operator in JavaScript
• Left Shift (
• Right Shift (>>) Bitwise Operator in JavaScript
• Zero Fill Right Shift (>>>) Bitwise Operator in JavaScript

JS Unary Operators

• JavaScript typeof Operator
• JavaScript delete Operator

JS Relational Operators

• JavaScript in Operator
• JavaScript Instanceof Operator

JS Other Operators

• JavaScript String Operators
• JavaScript yield Operator
• JavaScript Pipeline Operator
• JavaScript Grouping Operator

AND(&&) Logical Operator in JavaScript

The logical AND (&&) (logical conjunction) operator for a set of boolean operands will be true if and only if all the operands are true. Otherwise, it will be false. It’s commonly used to combine conditions in conditional statements or to check multiple conditions before executing code.

The Logical AND(&&) Operator can also be used on non-boolean values also. AND operator has higher precedence than the OR operator.

Example 1: In this example, we will use the AND operator on normal values.

Example 2: In this example, we will use the AND operator on function calls

Supported Browsers:

• Google Chrome
• Edge  

We have a complete list of JavaScript Logical Operators, to learn about those please go through JavaScript Logical Operator article.

Please Login to comment...

Similar reads.

• Web Technologies

Improve your Coding Skills with Practice

What kind of Experience do you want to share?

JS Tutorial

Js versions, js functions, js html dom, js browser bom, js web apis, js vs jquery, js graphics, js examples, js references, javascript operators.

Javascript operators are used to perform different types of mathematical and logical computations.

The Assignment Operator = assigns values

The Addition Operator + adds values

The Multiplication Operator * multiplies values

The Comparison Operator > compares values

JavaScript Assignment

The Assignment Operator ( = ) assigns a value to a variable:

Assignment Examples

Javascript addition.

The Addition Operator ( + ) adds numbers:

JavaScript Multiplication

The Multiplication Operator ( * ) multiplies numbers:

Multiplying

Types of javascript operators.

There are different types of JavaScript operators:

• Arithmetic Operators
• Assignment Operators
• Comparison Operators
• String Operators
• Logical Operators
• Bitwise Operators
• Ternary Operators
• Type Operators

JavaScript Arithmetic Operators

Arithmetic Operators are used to perform arithmetic on numbers:

Arithmetic Operators Example

Arithmetic operators are fully described in the JS Arithmetic chapter.

Advertisement

JavaScript Assignment Operators

Assignment operators assign values to JavaScript variables.

The Addition Assignment Operator ( += ) adds a value to a variable.

Assignment operators are fully described in the JS Assignment chapter.

JavaScript Comparison Operators

Comparison operators are fully described in the JS Comparisons chapter.

JavaScript String Comparison

All the comparison operators above can also be used on strings:

Note that strings are compared alphabetically:

JavaScript String Addition

The + can also be used to add (concatenate) strings:

The += assignment operator can also be used to add (concatenate) strings:

The result of text1 will be:

When used on strings, the + operator is called the concatenation operator.

Adding Strings and Numbers

Adding two numbers, will return the sum, but adding a number and a string will return a string:

The result of x , y , and z will be:

If you add a number and a string, the result will be a string!

JavaScript Logical Operators

Logical operators are fully described in the JS Comparisons chapter.

JavaScript Type Operators

Type operators are fully described in the JS Type Conversion chapter.

JavaScript Bitwise Operators

Bit operators work on 32 bits numbers.

The examples above uses 4 bits unsigned examples. But JavaScript uses 32-bit signed numbers. Because of this, in JavaScript, ~ 5 will not return 10. It will return -6. ~00000000000000000000000000000101 will return 11111111111111111111111111111010

Bitwise operators are fully described in the JS Bitwise chapter.

Test Yourself With Exercises

Multiply 10 with 5 , and alert the result.

Start the Exercise

Test Yourself with Exercises!

Exercise 1 »   Exercise 2 »   Exercise 3 »   Exercise 4 »   Exercise 5 »

COLOR PICKER

Contact Sales

If you want to use W3Schools services as an educational institution, team or enterprise, send us an e-mail: [email protected]

Report Error

If you want to report an error, or if you want to make a suggestion, send us an e-mail: [email protected]

Top Tutorials

Top references, top examples, get certified.

Learning JavaScript double question mark (??) or the Nullish Coalescing Operator

This operator is also known as the Nullish Coalescing Operator. It’s a new feature introduced in JavaScript ES2020 that allows you to check for null or undefined values in a more concise way.

Nullish Coalescing Operator syntax

Why javascript needed this operator, several use cases for the nullish coalescing operator, handling missing function arguments.

The Nullish Coalescing Operator can be used to provide default values for a missing argument as follows:

Accessing object properties

Choosing between a variable and a constant, using with || and && operators, take your skills to the next level ⚡️.

• Stack Overflow for Teams Where developers & technologists share private knowledge with coworkers
• Advertising & Talent Reach devs & technologists worldwide about your product, service or employer brand
• OverflowAI GenAI features for Teams
• OverflowAPI Train & fine-tune LLMs
• Labs The future of collective knowledge sharing
• About the company Visit the blog

Collectives™ on Stack Overflow

Find centralized, trusted content and collaborate around the technologies you use most.

Q&A for work

Connect and share knowledge within a single location that is structured and easy to search.

Get early access and see previews of new features.

Using ampersand in a javascript string

I have this code:

While using Javascript/JQuery I want to hide a few parts. However, the above code gives me a syntax error.

What do I do so I can compare the id from my listitem with the javascript string? I already tried switching the ampersand in javascript with things like "&amp ;" and "&#38 ;"

Since I get the id of the listitem from a database I'd prefer not to change that side.

• 8 An id cannot contain white-space characters; as to whether it might work with the white-space removed (making the id="test&test" ) I'm unsure, though I suspect it would, but you might have to escape the ampersand in your CSS selectors. –  David Thomas Commented Sep 20, 2016 at 12:58
• 1 ID and NAME tokens must begin with a letter ([A-Za-z]) and may be followed by any number of letters, digits ([0-9]) , hyphens ("-") , underscores ("_") , colons (":") , and periods (".") . –  Kurt Van den Branden Commented Sep 20, 2016 at 13:02
• 1 @KurtVandenBranden that is an old spec and not html5 spec –  charlietfl Commented Sep 20, 2016 at 13:04

2 Answers 2

You can't use spaces in the id of an element.

You probably don't want to use an ampersand in the id of an element, but if you really need to you can escape the & using one backslash in the css selector, and two backslashes in the jQuery selector.

In your example:

var array = ["test1", "test2", "test\\&test"]; $(document).ready(function() { for (i = 0; i < array.length; i++) { $("#" + array[i]).hide(); } }); <script src="https://ajax.googleapis.com/ajax/libs/jquery/2.0.0/jquery.min.js"></script> <ul> <li id="test1"></li> <li id="test2"></li> <li id="test&test"></li> </ul>

id CANNOT contain spaces

replace your id "test & test" with "test_test" and it will work.

or if you really need to use ampersand escape it in js array with \\

Your Answer

Reminder: Answers generated by artificial intelligence tools are not allowed on Stack Overflow. Learn more

Sign up or log in

Post as a guest.

Required, but never shown

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy .

Not the answer you're looking for? Browse other questions tagged javascript jquery html or ask your own question .

• Featured on Meta
• We've made changes to our Terms of Service & Privacy Policy - July 2024
• Announcing a change to the data-dump process

Hot Network Questions

• The Puzzle Noob’s New Game
• Can any analytic function be written as the difference of two monotonically increasing analytic functions?
• Understanding parallelStream and collector order
• Inserting a 0 in Specific Symbols
• How to become Emperor of the Galaxy
• Why do C++ sequence containers have an "assign" method but associative containers do not?
• Stuck in Infinite Loop
• Possibly manipulated recommendation letter - inform alleged author?
• Newtonian vs General Relativistic light deflection angle
• One Page IDP issued by Govt. Of India not acceptable in Japan
• Movie identification 90s-ish on the Syfy channel sea creature
• What is the difference between the complex numbers i and -i?
• Optimal strategy for determining unknown permutation given the number of correctly placed elements after each guess
• Lexicographically earliest permutation of the initial segment of nonnegative integers subject to divisibility constraints
• Is "Non-Trivial amount of work" a correct phrase?
• finite groups with fixed-point-free automorphisms of prime order
• Why doesn't Oppenheimer like the word "bomb" being used to describe the bomb?
• Does a router lookup in routing table twice for each packet?
• What are the specific terms for breaking up English words into roots/components
• Passport Renewals
• ORCA 6 slower than ORCA 5?
• Space UN – non human focalpoints
• Private sector professional being screened out of PhD program
• Why do doctors always seem to overcharge for services?

• Skip to main content
• Skip to search
• Skip to select language
• Sign up for free

Assignment (=)

The assignment ( = ) operator is used to assign a value to a variable or property. The assignment expression itself has a value, which is the assigned value. This allows multiple assignments to be chained in order to assign a single value to multiple variables.

A valid assignment target, including an identifier or a property accessor . It can also be a destructuring assignment pattern .

An expression specifying the value to be assigned to x .

Return value

The value of y .

Thrown in strict mode if assigning to an identifier that is not declared in the scope.

Thrown in strict mode if assigning to a property that is not modifiable .

Description

The assignment operator is completely different from the equals ( = ) sign used as syntactic separators in other locations, which include:

• Initializers of var , let , and const declarations
• Default values of destructuring
• Default parameters
• Initializers of class fields

All these places accept an assignment expression on the right-hand side of the = , so if you have multiple equals signs chained together:

This is equivalent to:

Which means y must be a pre-existing variable, and x is a newly declared const variable. y is assigned the value 5 , and x is initialized with the value of the y = 5 expression, which is also 5 . If y is not a pre-existing variable, a global variable y is implicitly created in non-strict mode , or a ReferenceError is thrown in strict mode. To declare two variables within the same declaration, use:

Simple assignment and chaining

Value of assignment expressions.

The assignment expression itself evaluates to the value of the right-hand side, so you can log the value and assign to a variable at the same time.

Unqualified identifier assignment

The global object sits at the top of the scope chain. When attempting to resolve a name to a value, the scope chain is searched. This means that properties on the global object are conveniently visible from every scope, without having to qualify the names with globalThis. or window. or global. .

Because the global object has a String property ( Object.hasOwn(globalThis, "String") ), you can use the following code:

So the global object will ultimately be searched for unqualified identifiers. You don't have to type globalThis.String ; you can just type the unqualified String . To make this feature more conceptually consistent, assignment to unqualified identifiers will assume you want to create a property with that name on the global object (with globalThis. omitted), if there is no variable of the same name declared in the scope chain.

In strict mode , assignment to an unqualified identifier in strict mode will result in a ReferenceError , to avoid the accidental creation of properties on the global object.

Note that the implication of the above is that, contrary to popular misinformation, JavaScript does not have implicit or undeclared variables. It just conflates the global object with the global scope and allows omitting the global object qualifier during property creation.

Assignment with destructuring

The left-hand side of can also be an assignment pattern. This allows assigning to multiple variables at once.

For more information, see Destructuring assignment .

Specifications

Browser compatibility

BCD tables only load in the browser with JavaScript enabled. Enable JavaScript to view data.

• Assignment operators in the JS guide
• Destructuring assignment