JavaScript object built-in objects, value types and reference types explained

// Non-null object:
var object name = {
	Property name: value,
	...
	Method name: function([parameters]){
		Method body statements;
	}
	...
}

var p1 = {
	color: 'black', //Add attributes to the object weight: '188g', //Attributes are separated by commas screenSize: 6.5,
	call: function(name){//Add method to the object console.log("Outgoing call: "+name);
	},
	sendMassage: function(msg){
		console.log("The message sent is: "+msg);
	},
	playVideo: function(){
		console.log("play video");
	},
	playMusic: function(){
		console.log("playing music");
	}
}
console.log("Mobile phone color:"+p1['color']); //You can also use object['property'] to output property values ​​console.log("Mobile phone weight:"+p1.weight);
console.log("Screen size:"+p1.screenSize);
p1.call("张三");//Call the object's sending method p1["sendMassage"]("helo");
p1.playVideo();
p1.playMusic();
console.log(p1);

var p = new Object(); // Create an empty object p

p2.name = 'Liu Bei';
p2.sex = 'male';
p2.age = 32;
p2.sayHello = function(){
	console.log('Hello');
}
p2.sayHello(); //Call object method

function Student(name,sex,age){
	this.name = name; //This refers to the newly created object of the constructor this.sex = sex;
	this.age = age;
	this.show = function(){
		console.log("Name: "+this.name)
		console.log("Sex: "+this.sex)
		console.log("Age: "+this.age)
	}
}
var s1 = new Student('乔峰','男',28);//s1 is a new object created by the constructor, i.e., an instance s1.show();
var s2 = new Student('段煜','男',23);
s2.show();

for(var variable name in object name){
	Loop Statement}

function Student(name,sex,age){
	this.name = name;
	this.sex = sex;
	this.age = age;
	this.show = function(){
		console.log("Name: "+this.name)
		console.log("Sex: "+this.sex)
		console.log("Age: "+this.age)
	}
}
// s2 is the object to be traversed var s2 = new Student('段煜','男',23);
for(var k in s2){
	console.log(k);//output name sex age show()
	console.log(s2[k]); // Output Duan Yunan 23 in sequence 
}

Math object: no need to instantiate Math.PI: arithmetic constant PI
Math.abs(x): Returns the absolute value of xMath.max(args...): Returns the maximum numberMath.min(args...): Returns the minimum numberMath.pow(x,y): Returns x raised to the power of yMath.sqrt(x): Returns the square root of xMath.random(): Returns a random number between 0.0 and 1.0Math.round(x): Returns the integer closest to xMath.floor(x): Returns an integer less than or equal to x and closest to itMath.ceil(x): Returns an integer greater than or equal to x and closest to it

// 1. Create a Date object without parameters var date1 = new Date();
console.log(date1);
// 2. Create a Date object with the specified date and time by passing in the year, month, day, hour, minute, and second. // Month is 0-11
var date2 = new Date(2021,4,22,10,17,55);
console.log(date2);
// 3. Pass in a date and time string to create a Date object var date3 = new Date("2021-5-22 18:19:25");
console.log(date3);
console.log(date3.getMonth()) //4
console.log(date3.getTime()) // represents the number of milliseconds between the Date object and midnight on January 1, 1970 console.log(date1.toLocaleDateString()) // 2021/6/14
console.log(date1.toLocaleString()) //2021/6/14 11:17:36 PM
console.log(date1.getFullYear())//2021

- charAt(n) returns the string at position n - concat(s1,s2,...) concatenates multiple strings - charCodeAt(n) returns the ASCII code at position n - split('separator') converts a string into a string array according to the given separator - substr(start,length) extracts length characters from start to form a new string - substring(from,to) extracts the string between from and to to form a new string - toLowerCase() converts uppercase characters in a string to lowercase without affecting the original string and returns a new string - toUpperCase() converts all lowercase characters in a string to uppercase without affecting the original string and returns a new string - replace(str1,str2) replaces str1 in a string with str2 and returns the replacement result without affecting the original string

// Input a string of letters and count the number of times each letter appears in the string var str = 'abBSdXbdea';
var lower = new Array(26);//Store the number of times each of the 26 lowercase letters appears var upper = new Array(26);//Store the number of times each of the 26 uppercase letters appears // Initialize two arrays for(var i=0;i<lower.length;i++){
    lower[i] = 0
    upper[i] = 0
}
for(var k=0;k<str.length;k++){
    if(str.charAt(k)>='a' && str.charAt(k)<='z'){
        lower[str.charCodeAt(k)-97]++
    }else if(str.charAt(k)>='A' && str.charAt(k)<='Z'){
        upper[str.charCodeAt(k)-65]++
    }
}
console.log(lower);
console.log(upper);

/* Input a decimal integer and a number system (2, 8, 16) and convert the decimal integer into the corresponding numerical format and output the remainder method:
               m=15 k=8
               m%k stores the remainder in an array*/
        var m = parseInt(prompt('Please enter an integer:'));
        var k = parseInt(prompt('Please enter a number system (2~16)'));
        var result = ['0','1','2','3','4','5','6','7','8','9','A','B','C','D','E','F'];
        var arr = new Array(); //Store the result of number system conversion var i = 0;
        while(m!=0){//Convert m to a number system and put the remainder in the arr array arr[i] = m%k;
            m = parseInt(m/k);
            i++;
        }
        var str = '';
        if(k==8){
            str = '0';
        }else if(k==16){
            str = '0x';
        }
        for(var i=arr.length-1;i>=0;i--){
            str += result[arr[i]];
        }
        console.log('The result of the conversion is: '+str);