javascript (typeof variable === "function") 和 jQuery.isFunction() 有什么区别？

What's the difference between (typeof variable === "function") and jQuery.isFunction()?

提问by Aust

I have always used (typeof variable === "function")and I stumbled across jQuery.isFunction()and I was wondering:

我一直在使用(typeof variable === "function")，我偶然发现jQuery.isFunction()，我想知道：

1. What is the difference between the typeof method and jQuery's method? And not only what the difference is, but
2. When is it appropriate to use the typeof method and when is it appropriate to use jQuery's method?

1. typeof方法和jQuery的方法有什么区别？不仅有什么不同，还有
2. 什么时候用typeof方法合适，什么时候用jQuery的方法合适？

回答by Lusitanian

There is almostno difference, other than that using jQuery is slightly slower. See the source code:

目前几乎没有区别，比使用jQuery等稍慢。查看源代码：

isFunction: function( obj ) {
    return jQuery.type(obj) === "function";
},

which calls a function which calls another function to determine the exactsame thing as what you showed :P

它调用一个函数，该函数调用另一个函数来确定与您显示的内容完全相同的内容：P

There is literally no advantage to jQuery in this case [or for that manner, 90% of the use-cases of the library]. Look into Vanilla-JSand check out some of its features :P

在这种情况下，jQuery 几乎没有任何优势 [或者对于这种情况，库的 90% 的用例]。查看Vanilla-JS并查看它的一些功能：P

TLDR: Don't use jQuery for this...or anything.

TLDR：不要为此使用jQuery……或任何东西。

UPDATE

更新

Here's a benchmark showing you that Vanilla JS is roughly 93% faster than jQuery: http://jsperf.com/jquery-isfunction-vs-vanilla-is-function.

这是一个基准，向您展示 Vanilla JS 比 jQuery 快大约 93%：http: //jsperf.com/jquery-isfunction-vs-vanilla-is-function。

回答by 0x499602D2

There's no difference. jQuery uses the same concept:

没有区别。jQuery 使用相同的概念：

// ...
isFunction: function( obj ) {
    return jQuery.type(obj) === "function";
}

Update:

更新：

After digging in deeper I found that jQuery's isFunctionmethod is comparing the toStringmethod of the Object.prototypechain on function() {}, to the string [object Function]. This is the how it differs from your former example and the reason for it being slower than typeof.

在深入挖掘之后，我发现 jQuery 的isFunction方法是将链上的toString方法与字符串进行比较。这就是它与您之前的示例的不同之处以及它比.Object.prototypefunction() {}[object Function]typeof

回答by JohnB

The jQuery source code for isFunction is

isFunction 的 jQuery 源代码是

isFunction: function( obj ) {
    return jQuery.type(obj) === "function";
},

type: function( obj ) {
return obj == null ?
   String( obj ) :
   class2type[ core_toString.call(obj) ] || "object";
},

//...

jQuery.each("Boolean Number String Function Array Date RegExp Object".split(" "),
   function(i, name) {
      class2type[ "[object " + name + "]" ] = name.toLowerCase();
});

core_toString = Object.prototype.toString,

hence jQuery.isFunctionreturns true if and only if calling Object.prototype.toString.callon its argument returns [object Function].

因此jQuery.isFunction当且仅当调用Object.prototype.toString.call其参数返回true [object Function]。

回答by Yuan Yuan

Usually you can test whether JS object is function by using this test:

通常你可以通过这个测试来测试JS对象是否是函数：

(typeof fn === 'function')

However, this doesn't always work (IE8):

但是，这并不总是有效（IE8）：

typeof alert => 'object'
typeof document.createElement('input').getAttribute => 'object'

Before jQuery 1.4 internally they used the same check, but now they've fixed it. So to be sure that passed object is a function which can be called, just use $.isFunction method:

在 jQuery 1.4 之前，他们在内部使用相同的检查，但现在他们已经修复了它。所以要确保传递的对象是一个可以调用的函数，只需使用 $.isFunction 方法：

$.isFunction(function() {}) => true
$.isFunction(alert) => true
$.isFunction(document.createElement('input').getAttribute) => true

Copied from this blog: http://nuald.blogspot.co.uk/2012/07/why-jqueryisfunction.html

复制自此博客：http: //nuald.blogspot.co.uk/2012/07/why-jqueryisfunction.html

回答by Greg Ross

The difference is that JQuery calls something equivalent to the following and checks for the "Function" string token:

不同之处在于 JQuery 调用与以下等效的内容并检查“Function”字符串标记：

var toString = Object.prototype.toString;
var func = function(){};

console.log(toString.call(func)); // "returns [object Function]"

Whereas typof, just returns "function":

而typof，只返回“函数”：

var fType = typeof func; 

console.log(fType); // returns "function"

Here's an example.

这是一个例子。