Function

arg1, arg2, ... argN

function 的引數名稱必須要符合正規的命名。每個名稱都必須要是有效的 JavaScript 識別符號規則的字串，或是使用英文逗號「, 」分隔開的字串清單; 像是 "x", "theValue", 或是 "a, b'。

functionBody

包含 JavaScript 狀態以及 function 定義的字串。

Function objects created with the Function constructor are parsed when the function is created. This is less efficient than declaring a function with a function expression (en-US) or function statement (en-US) and calling it within your code, because such functions are parsed with the rest of the code.

All arguments passed to the function are treated as the names of the identifiers of the parameters in the function to be created, in the order in which they are passed.

Invoking the Function constructor as a function (without using the new operator) has the same effect as invoking it as a constructor.

The global Function object has no methods or properties of its own, however, since it is a function itself it does inherit some methods and properties through the prototype chain from Function.prototype.

Function.prototype.arguments (en-US) 已棄用 非標準

An array corresponding to the arguments passed to a function. This is deprecated as a property of Function. Use the arguments object (available within the function) instead.

Function.prototype.caller (en-US) 非標準 已棄用

Specifies the function that invoked the currently executing function. This property is deprecated, and is only functional for some non-strict functions.

Function.prototype.displayName (en-US) 非標準 選擇性

The display name of the function.

Function.prototype.length

Specifies the number of arguments expected by the function.

Function.prototype.name (en-US)

The name of the function.

Function.prototype.prototype

Used when the function is used as a constructor with the new operator. It will become the new object's prototype.

Function.prototype.apply()

Calls a function with a given this value and optional arguments provided as an array (or an array-like object).

Function.prototype.bind()

Creates a new function that, when called, has its this keyword set to a provided value, optionally with a given sequence of arguments preceding any provided when the new function is called.

Function.prototype.call()

Calls a function with a given this value and optional arguments.

Function.prototype.toString() (en-US)

Returns a string representing the source code of the function. Overrides the Object.prototype.toString (en-US) method.

Function instances inherit methods and properties from Function.prototype. As with all constructors, you can change the constructor's prototype object to make changes to all Function instances.

The following code creates a Function object that takes two arguments.

// Example can be run directly in your JavaScript console

// Create a function that takes two arguments and returns the sum of those arguments
var adder = new Function('a', 'b', 'return a + b');

// Call the function
adder(2, 6);
// > 8

The arguments "a" and "b" are formal argument names that are used in the function body, "return a + b".

Functions created with the Function constructor do not create closures to their creation contexts; they always are created in the global scope. When running them, they will only be able to access their own local variables and global ones, not the ones from the scope in which the Function constructor was called. This is different from using eval (en-US) with code for a function expression.

var x = 10;

function createFunction1() {
    var x = 20;
    return new Function('return x;'); // this |x| refers global |x|
}

function createFunction2() {
    var x = 20;
    function f() {
        return x; // this |x| refers local |x| above
    }
    return f;
}

var f1 = createFunction1();
console.log(f1());          // 10
var f2 = createFunction2();
console.log(f2());          // 20

• Functions and function scope
• Function
• function statement (en-US)
• function expression (en-US)
• function* statement
• function* expression (en-US)
• GeneratorFunction (en-US)