JavaScript learning

title: Javascript
tags: javascript, learning
grammar_cjkRuby: true
---

Define variables

Three forms

var name;
var name = "zhang san";
var name; name = "zhang san";

Data types of Javascript

6 data types

String
Single quotes or double quotes

var name = "zhang san";
var name = 'zhang san';

Number
Calculation, counting

var cost = 8.32;

boolean
The value can only be true or false;

var yes = true; 
var no = false;

Array
An index array is a series of different data items, and the data is accessed through the subscript index array[index];

var array = ['hp','apple','lenovo'];
var apple = array[1];

Object
js object, similar to java class, can have its own attributes; can be accessed through 'object.property';

var stu = {"id":1,"name":"zhang san"};
var name = stu.name;

null
has no value

var a = null;

==Javascript is an implicit language and does not need to specify data Type, the interpreter will automatically analyze the correct data type==
In addition, you can assign one data type to another data type, such as

var id = "测试id"; 
id = 1;

arithmetic operator

var a = 9;
var b = a++;
//结果 a=10 b=9

var a = 5;
a += 5;
//a = 6

comparison operation Symbol

Use of array

Create array

var t1 = ['zhang','li'];

var t2 = new Array();
t2[0] = 'zhang' ;
t2[1] = 'li' ;

var t3 = new Array();
t3.push('zhang');
t3.push('li');

Operation method

Use of string

Escape characters

Operation string

var str = '今天是祖国的67岁生日';
alert(str.substring(3,9));

from Define object

var user = new object();
user.name = "zhang";
user.age = 18;