在我的开发工作中经常会遇到需要判断一个函数是否是JavaScript原生函数的情况，有时候这是一个很必要的工作，你需要知道这个函数是浏览器自身提供的，还是由第三方封装、伪装成原生函数。当然，最好的方法是考察执行这个函数的toString方法的返回值。

The JavaScript

完成这个任务的方法非常简单：

复制代码 代码如下:

function isNative(fn) {

return (/{s*[native code]s*}/).test('' + fn);

}

toString方法会返回这个方法的字符串形式，然后用正则表达式判断里面包含的字符。

更强悍的方法

Lodash的创始人John-David Dalton找到了一个更佳的方案:

复制代码 代码如下:

;(function() {

// Used to resolve the internal `[[Class]]` of values

var toString = Object.prototype.toString;

// Used to resolve the decompiled source of functions

var fnToString = Function.prototype.toString;

// Used to detect host constructors (Safari > 4; really typed array specific)

var reHostCtor = /^[object .+?Constructor]$/;

// Compile a regexp using a common native method as a template.

// We chose `Object#toString` because there's a good chance it is not being mucked with.

var reNative = RegExp('^' +

// Coerce `Object#toString` to a string

String(toString)

// Escape any special regexp characters

.replace(/[.*+?^${}()|[]/]/g, '$&')

// Replace mentions of `toString` with `.*?` to keep the template generic.

// Replace thing like `for ...` to support environments like Rhino which add extra info

// such as method arity.

.replace(/toString|(function).*?(?=()| for .+?(?=])/g, '$1.*?') + '$'

);

function isNative(value) {

var type = typeof value;

return type == 'function'

// Use `Function#toString` to bypass the value's own `toString` method

// and avoid being faked out.

? reNative.test(fnToString.call(value))

// Fallback to a host object check because some environments will represent

// things like typed arrays as DOM methods which may not conform to the

// normal native pattern.

: (value && type == 'object' && reHostCtor.test(toString.call(value))) || false;

}

// export however you want

module.exports = isNative;

}());

现在你也看到了，很复杂，但更强大。当然，这不是为了做安全防护，它只是给你提供是否是原生函数的相关信息。