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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.
Living Standard  

Browser compatibility

FeatureChromeEdgeFirefoxInternet ExplorerOperaSafari
Legacy generator function No No2 — 58 No No No
async function55 Yes52 No4210.1
block Yes Yes Yes Yes Yes Yes
break Yes Yes Yes Yes Yes Yes
class42 Yes45 No ?10.1
const21 Yes361 211 Yes5.1
continue Yes Yes Yes Yes Yes Yes
debugger Yes Yes Yes Yes Yes Yes
do...while Yes Yes Yes6 Yes Yes
Empty statement (;) Yes Yes Yes Yes Yes Yes
export61153544 No4710.1
for Yes Yes Yes Yes Yes Yes
for each...in No No1.5 — 57 No No No
for...in Yes Yes Yes6 Yes Yes
for...of3812135 No258
function Yes Yes Yes Yes Yes Yes
function*391326 No2610
if...else Yes Yes Yes Yes Yes Yes
import61153544 No4710.1
label Yes Yes Yes Yes Yes Yes
let4112446 7 8111710
return Yes Yes Yes Yes Yes Yes
switch Yes Yes Yes Yes Yes Yes
throw Yes Yes Yes Yes Yes Yes
try...catch Yes Yes Yes6 Yes Yes
var Yes Yes Yes Yes Yes Yes
while Yes Yes Yes Yes Yes Yes
with Yes Yes Yes Yes Yes Yes
FeatureAndroid webviewChrome for AndroidEdge mobileFirefox for AndroidIE mobileOpera AndroidiOS Safari
Legacy generator function No No No4 — 58 No No No
async function Yes55 Yes52 No4210.1
block Yes Yes Yes Yes Yes Yes Yes
break Yes Yes Yes Yes Yes Yes Yes
class4242 Yes45 No ?10.1
const Yes Yes Yes361 211 Yes Yes
continue Yes Yes Yes Yes Yes Yes Yes
debugger Yes Yes Yes Yes Yes Yes Yes
do...while Yes Yes Yes Yes Yes Yes Yes
Empty statement (;) Yes Yes Yes Yes Yes Yes Yes
export No61 Yes544 No4710.1
for Yes Yes Yes Yes Yes Yes Yes
for each...in No No No4 — 57 No No No
for...in Yes Yes Yes Yes Yes Yes Yes
for...of5.1 Yes12 Yes No258
function Yes Yes Yes Yes Yes Yes Yes
function* Yes39 Yes26 No Yes10
if...else Yes Yes Yes Yes Yes Yes Yes
import No61 Yes544 No4710.1
label Yes Yes Yes Yes Yes Yes Yes
let414112446 7 8 ?1710
return Yes Yes Yes Yes Yes Yes Yes
switch Yes Yes Yes Yes Yes Yes Yes
throw Yes Yes Yes Yes Yes Yes Yes
try...catch Yes Yes Yes Yes Yes Yes Yes
var Yes Yes Yes Yes Yes Yes Yes
while Yes Yes Yes Yes Yes Yes Yes
with Yes Yes Yes Yes Yes Yes Yes

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: 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. 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).

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

8. Firefox 54 adds support of let in workers.

See also

Documentlabels en -medewerkers

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