This chapter documents all the JavaScript language operators, expressions and keywords.

Expressions and operators by category

For an alphabetical listing see the sidebar on the left.

Primary expressions

Basic keywords and general expressions in JavaScript.

this
The this keyword refers to a special property of an execution context.
function
The function keyword defines a function expression.
class
The class keyword defines a class expression.
function*
The function* keyword defines a generator function expression.
yield
Pause and resume a generator function.
yield*
Delegate to another generator function or iterable object.
async function*
The async function defines an async function expression.
await
Pause and resume an async function and wait for the promise's resolution/rejection.
[]
Array initializer/literal syntax.
{}
Object initializer/literal syntax.
/ab+c/i
Regular expression literal syntax.
( )
Grouping operator.

Left-hand-side expressions

Left values are the destination of an assignment.

Property accessors
Member operators provide access to a property or method of an object
(object.property and object["property"]).
new
The new operator creates an instance of a constructor.
new.target
In constructors, new.target refers to the constructor that was invoked by new.
super
The super keyword calls the parent constructor.
...obj
Spread syntax allows an expression to be expanded in places where multiple arguments (for function calls) or multiple elements (for array literals) are expected.

Increment and decrement

Postfix/prefix increment and postfix/prefix decrement operators.

A++
Postfix increment operator.
A--
Postfix decrement operator.
++A
Prefix increment operator.
--A
Prefix decrement operator.

Unary operators

A unary operation is operation with only one operand.

delete
The delete operator deletes a property from an object.
void
The void operator discards an expression's return value.
typeof
The typeof operator determines the type of a given object.
+
The unary plus operator converts its operand to Number type.
-
The unary negation operator converts its operand to Number type and then negates it.
~
Bitwise NOT operator.
!
Logical NOT operator.

Arithmetic operators

Arithmetic operators take numerical values (either literals or variables) as their operands and return a single numerical value.

+
Addition operator.
-
Subtraction operator.
/
Division operator.
*
Multiplication operator.
%
Remainder operator.
**
Exponentiation operator.

Relational operators

A comparison operator compares its operands and returns a Boolean value based on whether the comparison is true.

in
The in operator determines whether an object has a given property.
instanceof
The instanceof operator determines whether an object is an instance of another object.
<
Less than operator.
>
Greater than operator.
<=
Less than or equal operator.
>=
Greater than or equal operator.

Note: => is not an operator, but the notation for Arrow functions.

Equality operators

The result of evaluating an equality operator is always of type Boolean based on whether the comparison is true.

==
Equality operator.
!=
Inequality operator.
===
Identity operator.
!==
Nonidentity operator.

Bitwise shift operators

Operations to shift all bits of the operand.

<<
Bitwise left shift operator.
>>
Bitwise right shift operator.
>>>
Bitwise unsigned right shift operator.

Binary bitwise operators

Bitwise operators treat their operands as a set of 32 bits (zeros and ones) and return standard JavaScript numerical values.

&
Bitwise AND.
|
Bitwise OR.
^
Bitwise XOR.

Binary logical operators

Logical operators are typically used with boolean (logical) values, and when they are, they return a boolean value.

&&
Logical AND.
||
Logical OR.

Conditional (ternary) operator

(condition ? ifTrue : ifFalse)

The conditional operator returns one of two values based on the logical value of the condition.

Assignment operators

An assignment operator assigns a value to its left operand based on the value of its right operand.

=
Assignment operator.
*=
Multiplication assignment.
/=
Division assignment.
%=
Remainder assignment.
+=
Addition assignment.
-=
Subtraction assignment
<<=
Left shift assignment.
>>=
Right shift assignment.
>>>=
Unsigned right shift assignment.
&=
Bitwise AND assignment.
^=
Bitwise XOR assignment.
|=
Bitwise OR assignment.
[a, b] = [1, 2]
{a, b} = {a:1, b:2}

Destructuring assignment allows you to assign the properties of an array or object to variables using syntax that looks similar to array or object literals.

Comma operator

,
The comma operator allows multiple expressions to be evaluated in a single statement and returns the result of the last expression.

Non-standard features

Legacy generator function
The function keyword can be used to define a legacy generator function inside an expression. To make the function a legacy generator, the function body should contains at least one yield expression.
Expression closures
The expression closure syntax is a shorthand for writing simple function.
[for (x of y) x]
Array comprehensions.
(for (x of y) y)
Generator comprehensions.

Specifications

Specification Status Comment
ECMAScript 1st Edition (ECMA-262)
The definition of 'Expressions' in that specification.
Standard Initial definition
ECMAScript 5.1 (ECMA-262)
The definition of 'Expressions' in that specification.
Standard  
ECMAScript 2015 (6th Edition, ECMA-262)
The definition of 'ECMAScript Language: Expressions' in that specification.
Standard New: Spread syntax, rest syntax, destructuring assignment, super keyword.
ECMAScript Latest Draft (ECMA-262)
The definition of 'ECMAScript Language: Expressions' in that specification.
Draft  

Browser compatibility

FeatureChromeEdgeFirefoxInternet ExplorerOperaSafari
Array comprehensions No No30 — 58 No No No
async function expression55 ?52 No4210.1
await55 Yes52 ?4210.1
class42 Yes45 No Yes Yes
Comma operator Yes Yes13 Yes Yes
Conditional operator (c ? t : f) Yes Yes1 Yes Yes Yes
delete Yes Yes1 Yes Yes Yes
Destructuring assignment4914413 No Yes8
Expression closures No No3 — 60 No No No
function Yes Yes1 Yes Yes Yes
function* Yes Yes26 No Yes10
Generator comprehensions No No30 — 58 No No No
Grouping operator () Yes Yes1 Yes Yes Yes
in Yes Yes1 Yes Yes Yes
instanceof Yes Yes1 Yes Yes Yes
Legacy generator function No No2 — 58 No No No
new Yes Yes1 Yes Yes Yes
new.target46 Yes41 No Yes Yes
Object initializer1 Yes11 Yes1
Pipeline operator (|>) No No584 No No No
Property accessors Yes Yes1 Yes Yes Yes
super42 Yes45 No Yes Yes
this Yes Yes1 Yes Yes Yes
typeof Yes Yes1 Yes Yes Yes
void Yes Yes1 Yes Yes Yes
yield39 Yes265 No Yes10
yield* Yes Yes275 No Yes10
FeatureAndroid webviewChrome for AndroidEdge mobileFirefox for AndroidOpera AndroidiOS SafariSamsung Internet
Array comprehensions No No No30 — 58 No No No
async function expression5555 ?524210.16.0
await5555 Yes524210.16.0
class4242 Yes45 Yes Yes4.0
Comma operator Yes Yes Yes4 Yes Yes Yes
Conditional operator (c ? t : f) Yes Yes Yes4 Yes Yes Yes
delete Yes Yes Yes4 Yes Yes Yes
Destructuring assignment494914413 Yes85.0
Expression closures No No No4 — 60 No No No
function Yes Yes Yes4 Yes Yes Yes
function* Yes Yes Yes26 Yes10 Yes
Generator comprehensions No No No30 — 58 No No No
Grouping operator () Yes Yes Yes4 Yes Yes Yes
in Yes Yes Yes4 Yes Yes Yes
instanceof Yes Yes Yes4 Yes Yes Yes
Legacy generator function No No No4 — 58 No No No
new Yes Yes Yes4 Yes Yes Yes
new.target4646 Yes41 Yes Yes5.0
Object initializer11 Yes4 Yes1 Yes
Pipeline operator (|>) No No No584 No No No
Property accessors Yes Yes Yes4 Yes Yes Yes
super4242 Yes45 Yes Yes4.0
this Yes Yes Yes4 Yes Yes Yes
typeof Yes Yes Yes4 Yes Yes Yes
void Yes Yes Yes4 Yes Yes Yes
yield3939 Yes265 Yes104.0
yield* Yes Yes Yes275 Yes10 Yes

1. From version 7.0.0: this feature is behind the --harmony runtime flag.

2. From version 5.0.0: this feature is behind the --harmony runtime flag.

3. Firefox provided a non-standard destructuring implementation from Firefox 2 to 40.

4. From version 58: this feature is behind the --enable-pipeline-operator compile flag.

5. Starting with Firefox 33, the parsing of the yield expression has been updated to conform with the ES2015 specification.

6. From version 0.12: this feature is behind the --harmony runtime flag.

See also