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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
andobject["property"]
). new
- The
new
operator creates an instance of a constructor. - new.target
- In constructors,
new.target
refers to the constructor that was invoked bynew
. 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.
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.
Binary logical operators
Logical operators are typically used with boolean (logical) values, and when they are, they return a boolean value.
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
- Expression closures Obsolete since Gecko 60
- The expression closure syntax is a shorthand for writing simple function.
- Legacy generator function Obsolete since Gecko 58
- 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 oneyield
expression. [for (x of y) x]
Obsolete since Gecko 58- Array comprehensions.
(for (x of y) y)
Obsolete since Gecko 58- 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
Desktop | Mobile | Server | ||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Array comprehensions | Chrome No support No | Edge No support No | Firefox No support 30 — 58 | IE No support No | Opera No support No | Safari No support No | WebView Android No support No | Chrome Android No support No | Edge Mobile No support No | Firefox Android No support 30 — 58 | Opera Android No support No | Safari iOS No support No | Samsung Internet Android No support No | nodejs No support No |
async function expression | Chrome Full support 55 | Edge Full support 15 | Firefox Full support 52 | IE No support No | Opera Full support 42 | Safari Full support 10.1 | WebView Android Full support 55 | Chrome Android Full support 55 | Edge Mobile Full support 15 | Firefox Android Full support 52 | Opera Android Full support 42 | Safari iOS Full support 10.1 | Samsung Internet Android Full support 6.0 | nodejs
Full support
7.6.0
|
await | Chrome Full support 55 | Edge Full support Yes | Firefox Full support 52 | IE ? | Opera Full support 42 | Safari Full support 10.1 | WebView Android Full support 55 | Chrome Android Full support 55 | Edge Mobile Full support Yes | Firefox Android Full support 52 | Opera Android Full support 42 | Safari iOS Full support 10.1 | Samsung Internet Android Full support 6.0 | nodejs
Full support
7.6.0
|
class | Chrome Full support 42 | Edge Full support Yes | Firefox Full support 45 | IE No support No | Opera Full support Yes | Safari Full support Yes | WebView Android Full support 42 | Chrome Android Full support 42 | Edge Mobile Full support Yes | Firefox Android Full support 45 | Opera Android Full support Yes | Safari iOS Full support Yes | Samsung Internet Android Full support 4.0 | nodejs
Full support
6.0.0
|
Comma operator | Chrome Full support Yes | Edge Full support Yes | Firefox Full support 1 | IE Full support 3 | Opera Full support Yes | Safari Full support Yes | WebView Android Full support Yes | Chrome Android Full support Yes | Edge Mobile Full support Yes | Firefox Android Full support 4 | Opera Android Full support Yes | Safari iOS Full support Yes | Samsung Internet Android Full support Yes | nodejs Full support Yes |
Conditional operator (c ? t : f ) | Chrome Full support Yes | Edge Full support Yes | Firefox Full support 1 | IE Full support Yes | Opera Full support Yes | Safari Full support Yes | WebView Android Full support Yes | Chrome Android Full support Yes | Edge Mobile Full support Yes | Firefox Android Full support 4 | Opera Android Full support Yes | Safari iOS Full support Yes | Samsung Internet Android Full support Yes | nodejs Full support Yes |
delete | Chrome Full support Yes | Edge Full support Yes | Firefox Full support 1 | IE Full support Yes | Opera Full support Yes | Safari Full support Yes | WebView Android Full support Yes | Chrome Android Full support Yes | Edge Mobile Full support Yes | Firefox Android Full support 4 | Opera Android Full support Yes | Safari iOS Full support Yes | Samsung Internet Android Full support Yes | nodejs Full support Yes |
Destructuring assignment | Chrome Full support 49 | Edge Full support 14 | Firefox
Full support
41
| IE No support No | Opera Full support Yes | Safari Full support 8 | WebView Android Full support 49 | Chrome Android Full support 49 | Edge Mobile Full support 14 | Firefox Android
Full support
41
| Opera Android Full support Yes | Safari iOS Full support 8 | Samsung Internet Android Full support 5.0 | nodejs Full support 6.0.0 |
Expression closures | Chrome No support No | Edge No support No | Firefox No support 3 — 60 | IE No support No | Opera No support No | Safari No support No | WebView Android No support No | Chrome Android No support No | Edge Mobile No support No | Firefox Android No support 4 — 60 | Opera Android No support No | Safari iOS No support No | Samsung Internet Android No support No | nodejs No support No |
function | Chrome Full support Yes | Edge Full support Yes | Firefox Full support 1 | IE Full support Yes | Opera Full support Yes | Safari Full support Yes | WebView Android Full support Yes | Chrome Android Full support Yes | Edge Mobile Full support Yes | Firefox Android Full support 4 | Opera Android Full support Yes | Safari iOS Full support Yes | Samsung Internet Android Full support Yes | nodejs Full support Yes |
function* | Chrome Full support Yes | Edge Full support Yes | Firefox Full support 26 | IE No support No | Opera Full support Yes | Safari Full support 10 | WebView Android Full support Yes | Chrome Android Full support Yes | Edge Mobile Full support Yes | Firefox Android Full support 26 | Opera Android Full support Yes | Safari iOS Full support 10 | Samsung Internet Android Full support Yes | nodejs Full support Yes |
Generator comprehensions | Chrome No support No | Edge No support No | Firefox No support 30 — 58 | IE No support No | Opera No support No | Safari No support No | WebView Android No support No | Chrome Android No support No | Edge Mobile No support No | Firefox Android No support 30 — 58 | Opera Android No support No | Safari iOS No support No | Samsung Internet Android No support No | nodejs No support No |
Grouping operator () | Chrome Full support Yes | Edge Full support Yes | Firefox Full support 1 | IE Full support Yes | Opera Full support Yes | Safari Full support Yes | WebView Android Full support Yes | Chrome Android Full support Yes | Edge Mobile Full support Yes | Firefox Android Full support 4 | Opera Android Full support Yes | Safari iOS Full support Yes | Samsung Internet Android Full support Yes | nodejs Full support Yes |
in | Chrome Full support Yes | Edge Full support Yes | Firefox Full support 1 | IE Full support Yes | Opera Full support Yes | Safari Full support Yes | WebView Android Full support Yes | Chrome Android Full support Yes | Edge Mobile Full support Yes | Firefox Android Full support 4 | Opera Android Full support Yes | Safari iOS Full support Yes | Samsung Internet Android Full support Yes | nodejs Full support Yes |
instanceof | Chrome Full support Yes | Edge Full support Yes | Firefox Full support 1 | IE Full support Yes | Opera Full support Yes | Safari Full support Yes | WebView Android Full support Yes | Chrome Android Full support Yes | Edge Mobile Full support Yes | Firefox Android Full support 4 | Opera Android Full support Yes | Safari iOS Full support Yes | Samsung Internet Android Full support Yes | nodejs Full support Yes |
Legacy generator function | Chrome No support No | Edge No support No | Firefox No support 2 — 58 | IE No support No | Opera No support No | Safari No support No | WebView Android No support No | Chrome Android No support No | Edge Mobile No support No | Firefox Android No support 4 — 58 | Opera Android No support No | Safari iOS No support No | Samsung Internet Android No support No | nodejs No support No |
new | Chrome Full support Yes | Edge Full support Yes | Firefox Full support 1 | IE Full support Yes | Opera Full support Yes | Safari Full support Yes | WebView Android Full support Yes | Chrome Android Full support Yes | Edge Mobile Full support Yes | Firefox Android Full support 4 | Opera Android Full support Yes | Safari iOS Full support Yes | Samsung Internet Android Full support Yes | nodejs Full support Yes |
new.target | Chrome Full support 46 | Edge Full support Yes | Firefox Full support 41 | IE No support No | Opera Full support Yes | Safari Full support Yes | WebView Android Full support 46 | Chrome Android Full support 46 | Edge Mobile Full support Yes | Firefox Android Full support 41 | Opera Android Full support Yes | Safari iOS Full support Yes | Samsung Internet Android Full support 5.0 | nodejs Full support 5.0.0 |
Object initializer | Chrome Full support 1 | Edge Full support Yes | Firefox Full support 1 | IE Full support 1 | Opera Full support Yes | Safari Full support 1 | WebView Android Full support 1 | Chrome Android Full support 18 | Edge Mobile Full support Yes | Firefox Android Full support 4 | Opera Android Full support Yes | Safari iOS Full support 1 | Samsung Internet Android Full support Yes | nodejs Full support Yes |
Pipeline operator (|> ) | Chrome No support No | Edge No support No | Firefox
Full support
58
| IE No support No | Opera No support No | Safari No support No | WebView Android No support No | Chrome Android No support No | Edge Mobile No support No | Firefox Android
Full support
58
| Opera Android No support No | Safari iOS No support No | Samsung Internet Android No support No | nodejs No support No |
Property accessors | Chrome Full support Yes | Edge Full support Yes | Firefox Full support 1 | IE Full support Yes | Opera Full support Yes | Safari Full support Yes | WebView Android Full support Yes | Chrome Android Full support Yes | Edge Mobile Full support Yes | Firefox Android Full support 4 | Opera Android Full support Yes | Safari iOS Full support Yes | Samsung Internet Android Full support Yes | nodejs Full support Yes |
super | Chrome Full support 42 | Edge Full support Yes | Firefox Full support 45 | IE No support No | Opera Full support Yes | Safari Full support Yes | WebView Android Full support 42 | Chrome Android Full support 42 | Edge Mobile Full support Yes | Firefox Android Full support 45 | Opera Android Full support Yes | Safari iOS Full support Yes | Samsung Internet Android Full support 4.0 | nodejs Full support Yes |
this | Chrome Full support Yes | Edge Full support Yes | Firefox Full support 1 | IE Full support Yes | Opera Full support Yes | Safari Full support Yes | WebView Android Full support Yes | Chrome Android Full support Yes | Edge Mobile Full support Yes | Firefox Android Full support 4 | Opera Android Full support Yes | Safari iOS Full support Yes | Samsung Internet Android Full support Yes | nodejs Full support Yes |
typeof | Chrome Full support Yes | Edge Full support Yes | Firefox Full support 1 | IE Full support Yes | Opera Full support Yes | Safari Full support Yes | WebView Android Full support Yes | Chrome Android Full support Yes | Edge Mobile Full support Yes | Firefox Android Full support 4 | Opera Android Full support Yes | Safari iOS Full support Yes | Samsung Internet Android Full support Yes | nodejs Full support Yes |
void | Chrome Full support Yes | Edge Full support Yes | Firefox Full support 1 | IE Full support Yes | Opera Full support Yes | Safari Full support Yes | WebView Android Full support Yes | Chrome Android Full support Yes | Edge Mobile Full support Yes | Firefox Android Full support 4 | Opera Android Full support Yes | Safari iOS Full support Yes | Samsung Internet Android Full support Yes | nodejs Full support Yes |
yield | Chrome Full support 39 | Edge Full support Yes | Firefox
Full support
26
| IE No support No | Opera Full support Yes | Safari Full support 10 | WebView Android Full support 39 | Chrome Android Full support 39 | Edge Mobile Full support Yes | Firefox Android
Full support
26
| Opera Android Full support Yes | Safari iOS Full support 10 | Samsung Internet Android Full support 4.0 | nodejs
Full support
4.0.0
|
yield* | Chrome Full support Yes | Edge Full support Yes | Firefox
Full support
27
| IE No support No | Opera Full support Yes | Safari Full support 10 | WebView Android Full support Yes | Chrome Android Full support Yes | Edge Mobile Full support Yes | Firefox Android
Full support
27
| Opera Android Full support Yes | Safari iOS Full support 10 | Samsung Internet Android Full support Yes | nodejs
Full support
4.0.0
|
Legend
- Full support
- Full support
- No support
- No support
- Compatibility unknown
- Compatibility unknown
- Experimental. Expect behavior to change in the future.
- Experimental. Expect behavior to change in the future.
- Non-standard. Expect poor cross-browser support.
- Non-standard. Expect poor cross-browser support.
- Deprecated. Not for use in new websites.
- Deprecated. Not for use in new websites.
- See implementation notes.
- See implementation notes.
- User must explicitly enable this feature.
- User must explicitly enable this feature.