Detailed explanation of several ways to detect data types in JavaScript

In the process of programming with javaScript, we often encounter such a problem, that is, we need to detect the type of a data or variable, this article This article mainly introduces a summary of several ways to detect data type in javaScript. Those who are interested can learn more.

In the process of programming with javaScript, we often encounter such a problem, that is, we need to detect the type of a data or variable. So what methods are provided for us in javaScript? There are a lot of codes circulating on the Internet, but I found that some of them were wrong, so I simply used each method myself. Today I specially sorted it out for future reference.

1. Typeof detection

typeof is a unary operator, syntax: typeof (operand), the operand can be of any type. Its return value is a string that describes the type of the operand.

// var arr = { name:"john"}; // object
  // var arr = ["语文","数学"]; // object
  // function Person() {};  // typeof(Person) => function
  // var arr = '我是字符串' ; // string
  // var arr = 66 ;    // number
  // var arr = true ;   // boolean
  // var arr = new Person(); // object
  // var arr = undefined;  // undefined
  // var arr = null;   // object
  // var arr = /^\d{5,20}$/; // object
  // console.log( typeof(arr) );

2. instanceof detection

instanceof detects whether a object is an instance of another object , can be used in the inheritance relationship to determine whether an instance belongs to its parent type.

// var arr = '我是字符串' ;   　　// console.log( arr instanceof String ) => false
    // var arr = 66 ;      　　 // console.log( arr instanceof Number ) =>false
    // var arr = true ;     　　 // console.log( arr instanceof Boolean ) =>false
    // var arr = ["语文","数学"];　　 // console.log( arr instanceof Array ) =>true
    // var arr = { name:"john"}; 　　 // console.log( arr instanceof Object ) =>true
    // var arr = function Person(){}; //console.log(arr instanceof Function)=>true
    // var arr = undefined;      // console.log(arr instanceof Object)=>false
    // var arr = null;        // console.log(arr instanceof Object)=>false
    // var arr = /^\d{5,20}$/;    // console.log(arr instanceof RegExp)=>true

3. Object.prototype.toString.call detection

Use the native toString() method on Object.prototype to determine the data type. The usage method is as follows: Object.prototype.toString.call(value)

// var arr = '我是字符串' ;   //[object String]
    // var arr = 66 ;        //[object Number]
    // var arr = true ;       //[object Boolean]
    // var arr = ["语文","数学"];  //[object Array]
    // var arr = { name:"john"};  //[object Object]
    // var arr = function Person(){}; //[object Function]
    // var arr = undefined;      //[object Undefined]
    // var arr = null;         //[object Null]
    // var arr = /^\d{5,20}$/;     //[object RegExp]
    // console.log( Object.prototype.toString.call(arr) );

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