JavaScript type judgment code analysis_javascript skills

Copy code The code is as follows:

var is = function(obj,type){
var toString =Object.prototype.toString,undefined;
return obj===null&&type==='Null'||
obj===undefined&&type==='Undefined'||
toString.call(obj ).slice(8,-1)===type;
}
//In the original text, there are parentheses surrounding each logical AND operation, but according to the operator priority, the parentheses can be omitted
// The first line declares undefined. My personal understanding is to improve performance and avoid querying undefined in the top-level scope.

According to the explanation in ECMA-262, Object.prototype.toString() , will return the type of object instance and return a string in the format "[object ", class, and "]".
So intercept the 'class' value through slice, which is the type value.
The exceptions are null and undefined, because they return
[object Object] in IE
Standard browser [object Window].
So make a separate judgment.
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