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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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