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Function 建構函式可建立一個新的 Function 物件。在 JavaScript 中,所有的函式實際上都是 Function 物件。

語法

new Function ([arg1[, arg2[, ...argN]],] functionBody)

參數

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。

描述

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 or function statement 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.

Function 的屬性與方法

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 原型物件

屬性 Properties

Function.arguments
An array corresponding to the arguments passed to a function. This is deprecated as property of Function, use the arguments object available within the function instead.
Function.arity
Used to specifiy the number of arguments expected by the function, but has been removed. Use the length property instead.
Function.caller
Specifies the function that invoked the currently executing function.
Function.length
Specifies the number of arguments expected by the function.
Function.name
The name of the function.
Function.displayName
The display name of the function.
Function.prototype.constructor
Specifies the function that creates an object's prototype. See Object.prototype.constructor for more details.

方法 Methods

Function.prototype.apply()
Calls a function and sets its this to the provided value, arguments can be passed as an Array object.
Function.prototype.bind()
Creates a new function which, when called, has its this set to the provided value, with a given sequence of arguments preceding any provided when the new function was called.
Function.prototype.call()
Calls (executes) a function and sets its this to the provided value, arguments can be passed as they are.
Function.prototype.isGenerator()
Returns true if the function is a generator; otherwise returns false.
Function.prototype.toSource()
Returns a string representing the source code of the function. Overrides the Object.prototype.toSource method.
Function.prototype.toString()
Returns a string representing the source code of the function. Overrides the Object.prototype.toString method.

Function 實例

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.

範例

Specifying arguments with the Function constructor

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".

Difference between Function constructor and function declaration

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 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

規範

Specification Status Comment
ECMAScript 1st Edition (ECMA-262) Standard Initial definition. Implemented in JavaScript 1.0.
ECMAScript 5.1 (ECMA-262)
The definition of 'Function' in that specification.
Standard  
ECMAScript 2015 (6th Edition, ECMA-262)
The definition of 'Function' in that specification.
Standard  
ECMAScript 2017 Draft (ECMA-262)
The definition of 'Function' in that specification.
Draft  

瀏覽器相容性

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)

參見

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