JavaScript小技巧：如何檢測一個函數是否是JavaScript原生函數

在我的開發工作中經常會遇到需要判斷一個函數是否是JavaScript原生函數的情況，有時候這是一個很必要的工作，你需要知道這個函數是瀏覽器自身提供的，還是由第三方封裝、偽裝成原生函數。當然，最好的方法是考察執行這個函數的toString方法的返回值。

The JavaScript

完成這個任務的方法非常簡單：

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

toString方法會返回這個方法的字符串形式，然后用正則表達式判斷里面包含的字符。

更強悍的方法

Lodash的創始人John-David Dalton找到了一個更佳的方案:

;(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;
}());

現在你也看到了，很復雜，但更強大。當然，這不是為了做安全防護，它只是給你提供是否是原生函數的相關信息。

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