JavaScript determines whether an object is an Object or an Array

1.typeof operator. For several types of objects such as Function, String, Number, Undefined, etc., he is fully capable, but when it is Array

var arr=new Array("1","2","3","4","5"); 
alert(typeof(arr));

You will receive an object answer, which is a bit disappointing.
2.instanceof operator, the instanceof operator in JavaScript will return an A Boolean value indicating whether the object is an instance of a specific class.
Usage: result = object instanceof class, it’s still the array just now, try it again, um, it returns true successfully.

var arrayStr=new Array("1","2","3","4","5"); 
alert(arrayStr instanceof Array);

Small summary: It seems that the problem we discussed today has been answered, but in fact, shuttling between multiple frames will cause big problems .

Code

var iframe = document.createElement('iframe'); 
document.body.appendChild(iframe); 
xArray = window.frames[window.frames.length-1].Array; 
var arr = new xArray("1","2","3","4","5");//这个写法IE大哥下是不支持的，FF下才有 
alert(arr instanceof Array); // false 
alert(arr.constructor === Array); // false

The return result is two False, which is disappointing.

ECMA-262 wrote
Object.prototype.toString( ) When the toString method is called, the following steps are taken:
1. Get the [[Class]] property of this object.
2. Compute a string value by concatenating the three strings “[object “, Result (1), and “]”.
3. Return Result (2)
The above specification defines the behavior of Object.prototype.toString: first, obtain an internal property [[Class]] of the object, and then return an object similar to "[object Array]" string as the result (anyone who has read the ECMA standard should know that [[]] is used to represent attributes used internally in the language and not directly accessible from the outside, called "internal attributes"). Using this method, With call, we can obtain the internal attributes [[Class]] of any object, and then convert the type detection into string comparison to achieve our purpose. Let's first look at the description of Array in the ECMA standard:
ECMA-262 wrote
new Array([ item0[, item1 [,…]]])
The [[Class]] property of the newly constructed object is set to “Array”.
So taking advantage of this, the third method appears.
function isArray(obj) {
return Object.prototype.toString.call(obj) === '[object Array]';
} call changes the this reference of toString to the object to be detected, returns the string representation of this object, and then compares whether this string is '[object Array]' to determine whether it is an instance of Array. Maybe you want to ask, why not o.toString() directly? Well, although Array inherits from Object, it will also have a toString method, but this method may be rewritten and fail to meet our requirements, and Object.prototype is the butt of a tiger, and few people dare to touch it, so It can guarantee its "purity" to a certain extent:)
Different from the previous solutions, this method solves the problem of cross-frame object construction very well. After testing, the compatibility of major browsers is also very good, so you can use it with confidence. The good news is that many frameworks, such as jQuery, Base2, etc., plan to use this method to implement certain types of special objects, such as arrays, regular expressions, etc., without having to write them ourselves.

In addition, Ext3 has also been changed to this way of writing

isArray : function(v){ 
return toString.apply(v) === '[object Array]'; 
}