检测一个函数是否是JavaScript原生函数

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。