检测一个函数是否是JavaScript原生函数的小技巧

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。