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。

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