js function to determine whether it is an array: isArray()_javascript technique-JS Tutorial-php.cn

js function to determine whether it is an array: isArray()_javascript technique

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Release： 2016-05-16 18:00:03

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I just happened to be learning the Alipay JS framework base.js today. After taking a look, the implementation is like this:

Copy the code The code is as follows:

 
if (value instanceof Array || 
(!(value instanceof Object) && 
(Object.prototype.toString.call((value)) == '[object Array]') || 
typeof value.length = = 'number' && 
typeof value.splice != 'undefined' && 
typeof value.propertyIsEnumerable != 'undefined' && 
!value.propertyIsEnumerable('splice'))) { 
return 'array'; 
} 

How can I put it, it's chaotic. Of course, it can also be said to be "the most complete in history". It does use the most mainstream methods, but it just writes them all together.

As we know, using instanceof and constructor is the most direct and simple way:

Copy code The code is as follows:

 
var arr = []; 
arr instanceof Array; // true 
arr.constructor == Array; //true 

But, because Arrays created in different iframes do not share prototype. If used like this. Trouble begins. So, if you want to apply it in a framework, this method will definitely not work. On the contrary, this problem can be solved by using Douglas Crockford's cramming method ("JavaScript Language Essence" P61):

Copy code Code As follows:

 
var is_array = function(value) { 
return value && 
typeof value === 'object' && 
typeof value.length === 'number' && 
typeof value.splice === 'function' && 
!(value.propertyIsEnumerable('length')); 
}; 

However, are there any more What about the easy way? In fact, isn’t it just like what we use ourselves?

Copy code The code is as follows:

Object.prototype.toString.call(value) == '[object Array]'

The above writing method is what jQuery is using. Currently, Taobao’s kissy also uses this method. Isn't this the simplest and most effective way at present? Personally, I feel that the internal framework is a bit cumbersome to write. Routine summary, final solution:

Copy code The code is as follows:

 
var isArray = function( obj) { 
return Object.prototype.toString.call(obj) === '[object Array]'; 
} 
============== 

UPDATE: 2010.12.31 00:01 (Source)

Judge the type, cool. Specifically, it is the same as the above:

Copy the code The code is as follows:

 
var is = function (obj,type) { 
return (type === "Null" && obj === null) || 
(type === "Undefined" && obj === void 0 ) || 
(type === "Number" && isFinite(obj)) || 
Object.prototype.toString.call(obj).slice(8,-1) === type; 
} 