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JavaScript applications consist of statements with an appropriate syntax. A single statement may span multiple lines. Multiple statements may occur on a single line if each statement is separated by a semicolon. This isn't a keyword, but a group of keywords.

Statements and declarations by category

For an alphabetical listing see the sidebar on the left.

Control flow

Block
A block statement is used to group zero or more statements. The block is delimited by a pair of curly brackets.
break
Terminates the current loop, switch, or label statement and transfers program control to the statement following the terminated statement.
continue
Terminates execution of the statements in the current iteration of the current or labeled loop, and continues execution of the loop with the next iteration.
Empty
An empty statement is used to provide no statement, although the JavaScript syntax would expect one.
if...else
Executes a statement if a specified condition is true. If the condition is false, another statement can be executed.
switch
Evaluates an expression, matching the expression's value to a case clause, and executes statements associated with that case.
throw
Throws a user-defined exception.
try...catch
Marks a block of statements to try, and specifies a response, should an exception be thrown.

Declarations

var
Declares a variable, optionally initializing it to a value.
let
Declares a block scope local variable, optionally initializing it to a value.
const
Declares a read-only named constant.

Functions and classes

function
Declares a function with the specified parameters.
function*
Generators functions enable writing iterators more easily.
async function
Declares an async function with the specified parameters.
return
Specifies the value to be returned by a function.
class
Declares a class.

Iterations

do...while
Creates a loop that executes a specified statement until the test condition evaluates to false. The condition is evaluated after executing the statement, resulting in the specified statement executing at least once.
for
Creates a loop that consists of three optional expressions, enclosed in parentheses and separated by semicolons, followed by a statement executed in the loop.
for each...in
Iterates a specified variable over all values of object's properties. For each distinct property, a specified statement is executed.
for...in
Iterates over the enumerable properties of an object, in arbitrary order. For each distinct property, statements can be executed.
for...of
Iterates over iterable objects (including arrays, array-like objects, iterators and generators), invoking a custom iteration hook with statements to be executed for the value of each distinct property.
while
Creates a loop that executes a specified statement as long as the test condition evaluates to true. The condition is evaluated before executing the statement.

Others

debugger
Invokes any available debugging functionality. If no debugging functionality is available, this statement has no effect.
export
Used to export functions to make them available for imports in external modules, another scripts.
import
Used to import functions exported from an external module, another script.
label
Provides a statement with an identifier that you can refer to using a break or continue statement.
with
Extends the scope chain for a statement.

Specifications

Specification Status Comment
ECMAScript 1st Edition (ECMA-262)
The definition of 'Statements' in that specification.
Standard Initial definition
ECMAScript 3rd Edition (ECMA-262)
The definition of 'Statements' in that specification.
Standard  
ECMAScript 5.1 (ECMA-262)
The definition of 'Statements' in that specification.
Standard  
ECMAScript 2015 (6th Edition, ECMA-262)
The definition of 'ECMAScript Language: Statements and Declarations' in that specification.
Standard New: function*, let, for...of, yield, class
ECMAScript Latest Draft (ECMA-262)
The definition of 'ECMAScript Language: Statements and Declarations' in that specification.
Draft  

Browser compatibility

FunctieChromeEdgeFirefoxInternet ExplorerOperaSafari
Legacy generator function Nee Nee2 — 58 Nee Nee Nee
async function55 Ja52 Nee4210.1
block Ja Ja1 Ja Ja Ja
break Ja Ja1 Ja Ja Ja
class42 Ja45 Nee ?10.1
const21 Ja361 211 Ja5.1
continue Ja Ja1 Ja Ja Ja
debugger Ja Ja1 Ja Ja Ja
do...while Ja Ja16 Ja Ja
Empty statement (;) Ja Ja1 Ja Ja Ja
export61

16

153

60

54 — 604

Nee4710.1
for Ja Ja1 Ja Ja Ja
for each...in Nee Nee1.5 — 57 Nee Nee Nee
for...in Ja Ja16 Ja Ja
for...of3812135 Nee258
function Ja Ja1 Ja Ja Ja
function*391326 Nee2610
if...else Ja Ja1 Ja Ja Ja
import61

16

153

60

54 — 604

Nee4710.1
label Ja Ja1 Ja Ja Ja
let4112447 8 9111710
return Ja Ja1 Ja Ja Ja
switch Ja Ja1 Ja Ja Ja
throw Ja Ja1 Ja Ja Ja
try...catch Ja Ja16 Ja Ja
var Ja Ja1 Ja Ja Ja
while Ja Ja1 Ja Ja Ja
with Ja Ja1 Ja Ja Ja
FunctieAndroid webviewChrome for AndroidEdge mobileFirefox for AndroidOpera AndroidiOS SafariSamsung Internet
Legacy generator function Nee Nee Nee4 — 58 Nee Nee Nee
async function Ja55 Ja524210.16.0
block Ja Ja Ja4 Ja Ja Ja
break Ja Ja Ja4 Ja Ja Ja
class4242 Ja45 ?10.14.0
const Ja Ja Ja361 2 Ja Ja Ja
continue Ja Ja Ja4 Ja Ja Ja
debugger Ja Ja Ja4 Ja Ja Ja
do...while Ja Ja Ja4 Ja Ja Ja
Empty statement (;) Ja Ja Ja4 Ja Ja Ja
export Nee61 Ja

60

54 — 604

4710.1 Nee
for Ja Ja Ja4 Ja Ja Ja
for each...in Nee Nee Nee4 — 57 Nee Nee Nee
for...in Ja Ja Ja4 Ja Ja Ja
for...of5.1 Ja12145258 Ja
function Ja Ja Ja4 Ja Ja Ja
function* Ja39 Ja26 Ja104.0
if...else Ja Ja Ja4 Ja Ja Ja
import Nee61 Ja

60

54 — 604

4710.1 Nee
label Ja Ja Ja4 Ja Ja Ja
let414112447 8 917104.0
return Ja Ja Ja4 Ja Ja Ja
switch Ja Ja Ja4 Ja Ja Ja
throw Ja Ja Ja4 Ja Ja Ja
try...catch Ja Ja Ja4 Ja Ja Ja
var Ja Ja Ja4 Ja Ja Ja
while Ja Ja Ja4 Ja Ja Ja
with Ja Ja Ja4 Ja Ja Ja

1. Prior to Firefox 13, const is implemented, but re-assignment is not failing.

2. Prior to Firefox 46, a TypeError was thrown on redeclaration instead of a SyntaxError.

3. From version 15: this feature is behind the Experimental JavaScript Features preference.

4. From version 54 until version 60 (exclusive): this feature is behind the dom.moduleScripts.enabled preference. To change preferences in Firefox, visit about:config.

5. Prior to Firefox 51, using the for...of loop construct with the const keyword threw a SyntaxError ("missing = in const declaration").

6. From version 8: this feature is behind the --experimental-modules runtime flag.

7. Prior to Firefox 44, let is only available to code blocks in HTML wrapped in a <script type="application/javascript;version=1.7"> block (or higher version) and has different semantics (e.g. no temporal dead zone).

8. Prior to Firefox 46, a TypeError is thrown on redeclaration instead of a SyntaxError.

9. Firefox 54 adds support of let in workers.

See also

Documentlabels en -medewerkers

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