JavaScript小技巧：如何检测一个函数是否是JavaScript原生函数

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：

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:

;(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。

来自：http://www.webhek.com/detect-native-function/