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。


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


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'。


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.

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

{{page('/zh-TW/docs/JavaScript/Reference/Global_Objects/Function/prototype', 'Properties')}}

方法 Methods

{{page('/zh-TW/docs/JavaScript/Reference/Global_Objects/Function/prototype', 'Methods')}}

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.


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 (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


ECMAScript Language Specification
# sec-function-objects


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