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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
breakorcontinuestatement.
-
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
| Functie | Chrome | Edge | Firefox | Internet Explorer | Opera | Safari |
|---|---|---|---|---|---|---|
| Legacy generator function | Nee | Nee | 2 — 58 | Nee | Nee | Nee |
async function | 55 | Ja | 52 | Nee | 42 | 10.1 |
block | Ja | Ja | 1 | Ja | Ja | Ja |
break | Ja | Ja | 1 | Ja | Ja | Ja |
class | 42 | Ja | 45 | Nee | ? | 10.1 |
const | 21 | Ja | 361 2 | 11 | Ja | 5.1 |
continue | Ja | Ja | 1 | Ja | Ja | Ja |
debugger | Ja | Ja | 1 | Ja | Ja | Ja |
do...while | Ja | Ja | 1 | 6 | Ja | Ja |
Empty statement (;) | Ja | Ja | 1 | Ja | Ja | Ja |
export | 61 | 16 153 | 60 54 — 604 | Nee | 47 | 10.1 |
for | Ja | Ja | 1 | Ja | Ja | Ja |
for each...in | Nee | Nee | 1.5 — 57 | Nee | Nee | Nee |
for...in | Ja | Ja | 1 | 6 | Ja | Ja |
for...of | 38 | 12 | 135 | Nee | 25 | 8 |
function | Ja | Ja | 1 | Ja | Ja | Ja |
function* | 39 | 13 | 26 | Nee | 26 | 10 |
if...else | Ja | Ja | 1 | Ja | Ja | Ja |
import | 61 | 16 153 | 60 54 — 604 | Nee | 47 | 10.1 |
label | Ja | Ja | 1 | Ja | Ja | Ja |
let | 41 | 12 | 447 8 9 | 11 | 17 | 10 |
return | Ja | Ja | 1 | Ja | Ja | Ja |
switch | Ja | Ja | 1 | Ja | Ja | Ja |
throw | Ja | Ja | 1 | Ja | Ja | Ja |
try...catch | Ja | Ja | 1 | 6 | Ja | Ja |
var | Ja | Ja | 1 | Ja | Ja | Ja |
while | Ja | Ja | 1 | Ja | Ja | Ja |
with | Ja | Ja | 1 | Ja | Ja | Ja |
| Functie | Android webview | Chrome for Android | Edge mobile | Firefox for Android | Opera Android | iOS Safari | Samsung Internet |
|---|---|---|---|---|---|---|---|
| Legacy generator function | Nee | Nee | Nee | 4 — 58 | Nee | Nee | Nee |
async function | Ja | 55 | Ja | 52 | 42 | 10.1 | 6.0 |
block | Ja | Ja | Ja | 4 | Ja | Ja | Ja |
break | Ja | Ja | Ja | 4 | Ja | Ja | Ja |
class | 42 | 42 | Ja | 45 | ? | 10.1 | 4.0 |
const | Ja | Ja | Ja | 361 2 | Ja | Ja | Ja |
continue | Ja | Ja | Ja | 4 | Ja | Ja | Ja |
debugger | Ja | Ja | Ja | 4 | Ja | Ja | Ja |
do...while | Ja | Ja | Ja | 4 | Ja | Ja | Ja |
Empty statement (;) | Ja | Ja | Ja | 4 | Ja | Ja | Ja |
export | Nee | 61 | Ja | 60 54 — 604 | 47 | 10.1 | Nee |
for | Ja | Ja | Ja | 4 | Ja | Ja | Ja |
for each...in | Nee | Nee | Nee | 4 — 57 | Nee | Nee | Nee |
for...in | Ja | Ja | Ja | 4 | Ja | Ja | Ja |
for...of | 5.1 | Ja | 12 | 145 | 25 | 8 | Ja |
function | Ja | Ja | Ja | 4 | Ja | Ja | Ja |
function* | Ja | 39 | Ja | 26 | Ja | 10 | 4.0 |
if...else | Ja | Ja | Ja | 4 | Ja | Ja | Ja |
import | Nee | 61 | Ja | 60 54 — 604 | 47 | 10.1 | Nee |
label | Ja | Ja | Ja | 4 | Ja | Ja | Ja |
let | 41 | 41 | 12 | 447 8 9 | 17 | 10 | 4.0 |
return | Ja | Ja | Ja | 4 | Ja | Ja | Ja |
switch | Ja | Ja | Ja | 4 | Ja | Ja | Ja |
throw | Ja | Ja | Ja | 4 | Ja | Ja | Ja |
try...catch | Ja | Ja | Ja | 4 | Ja | Ja | Ja |
var | Ja | Ja | Ja | 4 | Ja | Ja | Ja |
while | Ja | Ja | Ja | 4 | Ja | Ja | Ja |
with | Ja | Ja | Ja | 4 | 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.