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    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
    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.
    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. 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

    Document Tags and Contributors

    Last updated by: fscholz,
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