Statements and declarations

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

Declarations

var (en-US)
Declares a variable, optionally initializing it to a value.
This is an experimental API that should not be used in production code. let (en-US)
Declares a block scope local variable, optionally initializing it to a value.
This is an experimental API that should not be used in production code. const (en-US)
Declares a read-only named constant.

Functions and classes

function (en-US)
Declares a function with the specified parameters.
This is an experimental API that should not be used in production code. function* (en-US)
Generators functions enable writing iterators more easily.
return (en-US)
Specifies the value to be returned by a function.
This is an experimental API that should not be used in production code. class (en-US)
Declares a class.

Iterations

do...while (en-US)
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 (en-US)
Creates a loop that consists of three optional expressions, enclosed in parentheses and separated by semicolons, followed by a statement executed in the loop.
This deprecated API should no longer be used, but will probably still work. This API has not been standardized. 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 (en-US)
Iterates over the enumerable properties of an object, in arbitrary order. For each distinct property, statements can be executed.
This is an experimental API that should not be used in production code. for...of (en-US)
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 (en-US)
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 (en-US)
Invokes any available debugging functionality. If no debugging functionality is available, this statement has no effect.
This is an experimental API that should not be used in production code. export (en-US)
Used to export functions to make them available for imports in external modules, another scripts.
This is an experimental API that should not be used in production code. import (en-US)
Used to import functions exported from an external module, another script.
label (en-US)
Provides a statement with an identifier that you can refer to using a break or continue statement.
This deprecated API should no longer be used, but will probably still work. with (en-US)
Extends the scope chain for a statement.

Specifications

Specification Status Comment
ECMAScript 1st Edition. Standard Initial definition.
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

See also