1. Common built-in objects

The so-called built-in objects are some objects provided by ECMAScript. We know that all objects have corresponding properties and methods.

1.1 Array

1.1.1 array creation method

Create in a literal way (recommended).

var colors = ['red','color','yellow'];

Use the constructor (later on) to create, and use the new keyword to create objects for the constructor.

var colors2 = new Array();

1.1.2 array assignment

var arr = [];
//One by one assignment by subscript
arr[0] = 123;
arr[1] = 'Ha ha ha';
arr[2] = 'Hey hey hey'

1.1.3 common methods of array

(1) concat(): array merging

var north = ['Beijing','Shandong','Tianjin'];
var south = ['Dongguan','Shenzhen','Shanghai'];
        
var newCity = north.concat(south);
console.log(newCity)

(2) join(): connect the elements in the array with the specified string, which will form a new string

var score = [98,78,76,100,0];
var str = score.join('|');
console.log(str);//98|78|76|100|0

(3) toString(): convert array to string

var score = [98,78,76,100,0];
//toString() Convert directly to a string using commas between each element
           
var str = score.toString();
console.log(str);//98,78,76,100,0

(4) slice(start,end): returns a segment of the array, left closed and right open

var arr = ['Zhang San','Li Si','Wang Wen','Zhao Liu'];
var newArr  = arr.slice(1,3);
console.log(newArr);//["Li Si", "Wang Wen"]

(5) pop(): delete the last element of the array and return the deleted element

var arr = ['Zhang San','Li Si','Wang Wen','Zhao Liu'];
var item = arr.pop();
console.log(arr);//["Zhang San", "Li Si"，"Wang Wen"]
console.log(item);//Zhao Liu

(6) push(): add one or more elements to the end of the array and return the new length

var arr = ['Zhang San','Li Si','Wang Wen','Zhao Liu'];
var newLength= arr.push('Little horse elder brother');//Multiple can be added, separated by commas
console.log(newLength);//5
console.log(arr);//["Zhang San", "Li Si"，"Wang Wen"，"Zhao Liu"，"Little horse elder brother"]

(7) reverse(): flip array

var names = ['alex','xiaoma','tanhuang','angle'];
       
//4.Inverted array
names.reverse();
console.log(names);

(8) sort(): sort an array

var names = ['alex','xiaoma','tanhuang','abngel'];
names.sort();
console.log(names)；// ["alex", "angle", "tanhuang", "xiaoma"]

(9) isArray(): judge whether it is an array

Boolean type value = array.isarray (detected value);

(10) shift(): delete and return the first element of the array

var arr = ['Zhang San','Li Si','Wang Wen','Zhao Liu'];
var a = arr.shift();
console.log(a); //Zhang San
console.log(arr); //['Li Si','Wang Wen','Zhao Liu']

(11) unshift(): adds one or more elements to the beginning of the array and returns the new length

var arr = ['Zhang San','Li Si','Wang Wen','Zhao Liu'];
var a = arr.unshift('Wang Wu');
console.log(a);  //5
console.log(arr);  //['Wang Wu','Zhang San','Li Si','Wang Wen','Zhao Liu']

1.2 common methods of String

String method:

(1) chartAt(): returns the character of the location of the specified index

var str = 'alex';
var charset = str.charAt(1);
console.log(charset);//l

(2) concat(): returns the string value, indicating the splicing of two or more strings

var str1 = 'al';
var str2  = 'ex';
console.log(str1.concat(str2,str2));//alexex

(3) replace(a,b): replace string a with string B

var a = '1234567755';
var newStr = a.replace("4567","****");
console.log(newStr);//123****755

(4) indexof(): find the subscript of the character. If the subscript of the returned string is found, return - 1. Same usage as the seal () method

var str = 'alex';
console.log(str.indexOf('e'));//2
console.log(str.indexOf('p'));//-1

(5) slice(start, end): extract a part of a string and return a new string. Left closed right split string

var str = 'Little horse elder brother';
console.log(str.slice(1,2));//Horse

(6) split('a',1): splits the string with string a and returns a new array. If the second parameter is not written, the whole array is returned. If the number is defined, the maximum length of the array is returned

var  str =  'My God?,a Right?,What are you talking about?a Ha ha ha';
console.log(str.split('a'));//["My God?,", "Right?,What are you talking about?", "Ha ha ha"]

(7) substr(start,length): returns the characters in a string from the specified position to the specified number of characters

var  str =  'My God?,a Right?,What are you talking about?a Ha ha ha';
console.log(str.substr(0,4));//My God?

(8) toLowerCase(): lower case

var str = 'XIAOMAGE';
console.log(str.toLowerCase())；//xiaomage

(9) toUpperCase(): capitalize

var str = 'xiaomage';
console.log(str.toUpperCase());

(10) substring(indexStart,indexEnd): extract the characters that the string mediates between two specified subscripts.

If indexStart equals indexEnd, substring returns an empty string.

If you omit indexEnd, substring extracts the character all the way to the end of the string.

If any parameter is less than 0 or is NaN, it is treated as 0.

If any parameter is greater than stringName.length, it is treated as stringName.length.

If indexStart is greater than indexEnd, the execution effect of substring is the same as two parameters swapped

(11) trim(): remove the white space on both sides of the string

The main application is user login registration, because the user input content cannot be predicted, and the space may be entered, so the input result can remove the blank.  

var str = '   xhh   ';
console.log(str);
console.log(str.trim());

1.3 Date object

There is only one way to create a date object, using the new keyword.

//Created a date object
var myDate = new Date();

//Create date object
var myDate=new Date();
        
//Get a day of the month
console.log(myDate.getDate());

//Return to local time
console.log(myDate().toLocalString());//2018/5/27 10 p.m.:36:23

Note: the above getxxx methods are all for obtaining time. If you want to set time and use setxxx, please refer to the link: https://www.runoob.com/jsref/jsref-obj-date.html

1.4 Math built in objects

Common built-in objects:

(1) Math.ceil() rounded up

var x = 1.234;
//Ceiling function is greater than or equal to x，And the nearest integer to it is 2
var a = Math.ceil(x);
console.log(a);//2

(2) Math.floor(): round down

var x = 1.234;
// Less than or equal to x，And the nearest integer 1
var b = Math.floor(x);
console.log(b);//1

(3) find the maximum and minimum of two numbers

//Find the maximum and minimum of two numbers
console.log(Math.max(2,5));//5
console.log(Math.min(2,5));//2

(4) random number: Math.random()

var ran = Math.random();
console.log(ran); //[0,1)

2. function

Function: encapsulate some statements, and then execute them in the form of calls.

console.log("hello world");
sayHello();     //Calling function
//Define function:
function sayHello(){
    console.log("hello");
    console.log("hello world");
}

2.1 definition of function

Syntax of function definition:

 Function function name (){

    }

Explain as follows:

2.2 function call

Syntax of function call:

 Function name ();

2.2.1 parameter of function: formal parameter and actual parameter

The parameters of a function include parameters and arguments

Note: the number of actual parameters and formal parameters should be the same.

Example:

sum(3,4);
sum("3",4);
sum("Hello","World");

//Functions: summing
function sum(a, b) {
    console.log(a + b);
}

2.2.2 return value of function

Example:

console.log(sum(3, 4));

//Functions: summing
function sum(a, b) {
    return a + b;
}