Detailed explanation of the seven data types in JavaScript

    //String
	let str = "hello js";
    console.log(str.toString); //Print: hello js
    console.log(str.length); //Print: 8
    console.log(str.substr(1,3));//Method: Split and print the string:ell
    console.log(str.split(' ')); //Method: print by grouping according to specified parameters ['hello' 'js']
    //Number
    let num = 123;
    console.log(!isNaN(num)); //Judge whether it is NaN, if not, it means it is a value //Boolean
    let flag = false;
    if(flag) { //The print result is false console.log("The result is true");
    }else{
        console.log("The result is false");
    }
    //Undefined
    let d;
    let val = `When an object is unassigned, its current value is: ${d}`;
    console.log(val); //Print: When an object is unassigned, the current value is: undefined
    //Null
    let a = null
    let nul = a;
    console.log(nul); //Print: null
    //Object
    let obj1 = {
        "name":"Zhang San",
        "age":24
    }
    //Symbol
    let sy = Symbol("1");
    if(sy == Symbol("1")) { //Print: the result is false console.log("the result is true");
    }else{
        console.log("The result is false");
    }