Summary of four methods of judging data type by js and jquery

1.typeof

typeof is an operator, which is used in two ways: typeof (expression) and typeof variable name, the first is to operate on expression, and the second is to operate on variable.

The results returned by this method are as follows:

Number, String, undefined, Bollean, Object, Function

The drawback is that if the data type is a reference data type, it can only return Object

console.log(typeof 1); //number
console.log(typeof true); //bollean
console.log(typeof ' Joy '); //string
console.log(typeof {}); //object
console.log(typeof []); //object

2.toString.call()

console.log(toString.call(666)); //[object Number]
console.log(toString.call(true)); //[object Boolean]
console.log(toString.call(' Joy ')); //[object String]
console.log(toString.call(undefined)); //[object Undefined]
console.log(toString.call({})); //[object Object]
console.log(toString.call([])); //[object Array]
console.log(toString.call(function(){})); //[object Function]

3.instanceof

In JavaScript, the typeof operator will be used to judge the type of a variable. When using typeof operator, there will be a problem when using reference type to store values. No matter what type of object is referenced, it will return "object". ECMAScript introduces another Java operator, instanceof, to solve this problem. The instanceof operator is similar to the typeof operator and is used to identify the type of object being processed. Unlike the typeof method, the instanceof method requires the developer to explicitly confirm that the object is of a specific type.

A instanceof B can judge whether A is an instance of B, return a Boolean value, and judge the data type by the construction type

console.log(arr instanceof Array ); // true
console.log(date instanceof Date ); // true
console.log(fn instanceof Function ); // true

4. Judging from the contructor of the object

console.log(arr.constructor === Array); //true
console.log(date.constructor === Date); //true
console.log(fn.constructor === Function); //true

Method for judging data type in JQuery

Returns 1 Boolean value

jQuery Object .isArray(); // Determine whether it is an array 
jQuery Object .isEmptyObject(); // Determine whether it is an empty object 
jQuery Object .isFunction(): // Determine whether it is a function 
jQuery Object .isNumberic(): // Determine whether it is a number 
jQuery Object .isWindow(): // Determine whether it is window Object 
jQuery Object .isXMLDoc(): // Judgment judgment 1 A DOM Whether the node is in the XML In the document 

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