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浏覽器自身提供的，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：
復制代碼 代碼如下:
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，然後用正則表達式判斷裡面包含的字符。
更強悍的方法
Lodash的創始人John-David Dalton找到了一個更佳的方案:
復制代碼 代碼如下:
;(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。