JS中的四种数据类型判断方法

// 字符串 
console.log(typeof('lili')); // string 
// 数字 
console.log(typeof(1)); // number 
// 布尔值 
console.log(typeof(true)); // boolean 
// undefined 
console.log(typeof(undefined)); // undefined 
// 对象 
console.log(typeof({})); // object 
// 数组 
console.log(typeof([])); // object 
// null 
console.log(typeof(null)); // object 
// 函数 
console.log(typeof(() => {})); // function 
// Symbol值 
console.log(typeof(Symbol())); // symbol 

object instanceof constructor 

const arr = [1, 2]; 
// 判断Object的prototype有没有在数组的原型链上 
console.log(arr instanceof Object); // true 
// 数组arr的原型 
const proto1 = Object.getPrototypeOf(arr); 
console.log(proto1); // [] 
// 数组arr的原型的原型 
const proto2 = Object.getPrototypeOf(proto1); 
console.log(proto2); // [] 
// Object的prototype 
console.log(Object.prototype); 
// 判断arr的原型是否与Object的prototype相等 
console.log(proto1 === Object.prototype); // false 
// 判断arr的原型的原型是否与Object的prototype相等 
console.log(proto2 === Object.prototype); // true 
 

const val1 = 1; 
console.log(val1.constructor); // [Function: Number] 
const val2 = 'abc'; 
console.log(val2.constructor); // [Function: String] 
const val3 = true; 
console.log(val3.constructor); // [Function: Boolean] 

function type(target) { 
    const ret = typeof(target); 
    const template = { 
        "[object Array]": "array",  
        "[object Object]":"object", 
        "[object Number]":"number - object", 
        "[object Boolean]":"boolean - object", 
        "[object String]":'string-object' 
    } 
    if(target === null) { 
        return 'null'; 
    } 
    else if(ret == "object"){ 
        const str = Object.prototype.toString.call(target); 
        return template[str]; 
    } 
    else{ 
        return ret; 
    } 
} 

console.log(type({})); // object 
console.log(type(123)); // number 
console.log(type('123')); // string