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    function

    The function declaration defines a function with the specified parameters.

    You can also define functions using the Function constructor and a function expression.

    Syntax

    function name([param,[, param,[..., param]]]) {
       [statements]
    }
    
    name
    The function name.
    param
    The name of an argument to be passed to the function. A function can have up to 255 arguments.
    statements
    The statements which comprise the body of the function.

    Description

    A function created with a function declaration is a Function object and has all the properties, methods and behavior of Function objects. See Function for detailed information on functions.

    A function can also be created using an expression (see function expression).

    By default, functions return undefined. To return any other value, the function must have a return statement that specifies the value to return.

    Conditionally created functions

    Functions can be conditionally declared, that is, a function statement can be nested within an if statement. Most browsers other than Mozilla will treat such conditional declarations as an unconditional declaration and create the function whether the condition is true or not, see this article for an overview. Therefore they should not be used, for conditional creation use function expressions.

    Function declaration hoisting

    Function declarations in JavaScript are hoisting the function definition. You can use the function before you declared it:

    hoisted(); // logs "foo"
    
    function hoisted() {
      console.log("foo");
    }
    

    Note that function expressions are not hoisted:

    notHoisted(); // TypeError: notHoisted is not a function
    
    var notHoisted = function() {
       console.log("bar");
    };
    

    Examples

    Using function

    The following code declares a function that returns the total amount of sales, when given the number of units sold of products a, b, and c.

    function calc_sales(units_a, units_b, units_c) {
       return units_a*79 + units_b * 129 + units_c * 699;
    }
    

    Specifications

    Specification Status Comment
    ECMAScript 1st Edition. Standard Initial definition. Implemented in JavaScript 1.0
    ECMAScript 5.1 (ECMA-262)
    The definition of 'Function definition' in that specification.
    Standard  
    ECMAScript 2015 (6th Edition, ECMA-262)
    The definition of 'Function definitions' in that specification.
    Standard  

    Browser compatibility

    Feature Chrome Firefox (Gecko) Internet Explorer Opera Safari
    Basic support (Yes) (Yes) (Yes) (Yes) (Yes)
    Feature Android Chrome for Android Firefox Mobile (Gecko) IE Mobile Opera Mobile Safari Mobile
    Basic support (Yes) (Yes) (Yes) (Yes) (Yes) (Yes)

    See also

    Document Tags and Contributors

    Last updated by: Nickolay,
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