Web front end -- JavaScript

Hee hee hee hee hee 2020-11-13 01:57:46
web end javascript


introduce JS

JavaScript Code must be at Between the labels .

Basic grammar
1. Variable var Variable name ='value';
2. JavaScript data type : A string value , The number , Boolean value , Array , object .
3. JavaScript function :
function myFunction(p1, p2) {
return p1 * p2;
} // This function returns p1 and p2 The product of the
4. Judge equal ?
==: Whether the values are equal
===: Whether the type and value are equal ;
5. Judgment statement
if( Conditions ){
Things that meet the conditions
Things that don't meet the conditions
6.for loop
for(var i=0; i<count; i++){
Loop operations }
Example of function
var info = " Open the success !";

 Insert picture description here

Attribute information of the tag object :
 innerHTML ---- Nested in the current tag object html Information
value --------- The information value entered by the user
src ------ Get the path of the picture , Modify the image path through assignment
checked ----- Determine whether the current multiple selection box is selected
js event

HTML The incident happened in HTML Things on the element .
When in HTML Page usage JavaScript when , JavaScript These events can be triggered .

 onsubmit --- Submit the incident
onclick ---- Click event
onfocus ----- Focus on events
onblur ------- Defocus event
onchange ---- What is executed when the object information changes
<button onclick="getElementById('demo').innerHTML=Date()">
The time is now ?
</button>// This statement applies a click event . When you click the statement, the current time will pop up .
What can application events do ?
 Events can be used to process form validation , User input , User behavior and browser action :
Event triggered on page load
Event triggered when the page is closed
The user clicks the button to perform the action
Verify the validity of user input
wait ...
DOM(document object model)

DOM (Document Object Model) Document object model , yes HTML and XML Documentation programming interface .
HTML DOM Defines access and operations HTML Standard approach to documentation .
DOM Express in tree structure HTML file .

stay HTML DOM (Document Object Model) in , Every element is node :

  • A document is a document node .
  • be-all HTML Elements are all element nodes .
  • all HTML Attributes are attribute nodes .
  • Text inserted into HTML Elements are text nodes .are text nodes.
  • Annotations are annotation nodes .
DOM Method
 document.getElementsByName --- It returns a list object
document.getElementById --- It returns an element object
document.createTextNode --- Create a text node
document.createElement --- Create an element node
NodeObj.appendChild --- Add a new child element to the element

Provincial and municipal secondary linkage

Code implementation
<!DOCTYPE html>
<html lang="en">
<meta charset="UTF-8">
function changeCity() {

var province = new Array(3);
province[0] = new Array('xian','xianyang','baoji');
province[1] = new Array('datong','taiyuan','yuncheng');
province[2] = new Array('guilin','nanning','liuzhou');
var choicepro = document.getElementById('province').value;
var selenode = document.getElementById('city');
var citys = province[choicepro];
selenode.length = 1;
for(var i=0;i<citys.length;i ++){

var textnode = document.createTextNode(citys[i]);
var optnode = document.createElement('option');
<div class="content">
<form action="#" method="get">
<span>ji guan</span>
<select id="province" onchange="changeCity()">
<option >---choice province---</option>
<option name="province" value="0">shaan xi</option>
<option name="province" value="1">shan xi</option>
<option name="province" value="2">guang xi</option>
<select id="city" >
<option>---choice city---</option>

 Insert picture description here

Dynamic addition

Code implementation
<!DOCTYPE html>
<html lang="en">
<meta charset="UTF-8">
function addCity() {

var city = document.getElementById('city').value;
if (city) {

var textnode = document.createTextNode(city);
var liElenode = document.createElement('li');
var ulElenode = document.getElementById('city_ul');
} else {

' City can't be empty \n'
<div class="content">
<input type="text" name="city" id="city" placeholder="Please input city">
<input type="button" value="add city" onclick="addCity()">
<ul id="city_ul">
<li>xi an</li>
<li>bei jing</li>

 Insert picture description here

本文为[Hee hee hee hee hee]所创,转载请带上原文链接,感谢

  1. [front end -- JavaScript] knowledge point (IV) -- memory leakage in the project (I)
  2. This mechanism in JS
  3. Vue 3.0 source code learning 1 --- rendering process of components
  4. Learning the realization of canvas and simple drawing
  5. gin里获取http请求过来的参数
  6. vue3的新特性
  7. Get the parameters from HTTP request in gin
  8. New features of vue3
  9. vue-cli 引入腾讯地图(最新 api,rocketmq原理面试
  10. Vue 学习笔记(3,免费Java高级工程师学习资源
  11. Vue 学习笔记(2,Java编程视频教程
  12. Vue cli introduces Tencent maps (the latest API, rocketmq)
  13. Vue learning notes (3, free Java senior engineer learning resources)
  14. Vue learning notes (2, Java programming video tutorial)
  15. 【Vue】—props属性
  16. 【Vue】—创建组件
  17. [Vue] - props attribute
  18. [Vue] - create component
  19. 浅谈vue响应式原理及发布订阅模式和观察者模式
  20. On Vue responsive principle, publish subscribe mode and observer mode
  21. 浅谈vue响应式原理及发布订阅模式和观察者模式
  22. On Vue responsive principle, publish subscribe mode and observer mode
  23. Xiaobai can understand it. It only takes 4 steps to solve the problem of Vue keep alive cache component
  24. Publish, subscribe and observer of design patterns
  25. Summary of common content added in ES6 + (II)
  26. No.8 Vue element admin learning (III) vuex learning and login method analysis
  27. Write a mini webpack project construction tool
  28. Shopping cart (front-end static page preparation)
  29. Introduction to the fluent platform
  30. Webpack5 cache
  31. The difference between drop-down box select option and datalist
  32. CSS review (III)
  33. Node.js学习笔记【七】
  34. Node.js learning notes [VII]
  35. Vue Router根据后台数据加载不同的组件(思考-&gt;实现-&gt;不止于实现)
  36. Vue router loads different components according to background data (thinking - & gt; Implementation - & gt; (more than implementation)
  37. 【JQuery框架,Java编程教程视频下载
  38. [jQuery framework, Java programming tutorial video download
  39. Vue Router根据后台数据加载不同的组件(思考-&gt;实现-&gt;不止于实现)
  40. Vue router loads different components according to background data (thinking - & gt; Implementation - & gt; (more than implementation)
  41. 【Vue,阿里P8大佬亲自教你
  42. 【Vue基础知识总结 5,字节跳动算法工程师面试经验
  43. [Vue, Ali P8 teaches you personally
  44. [Vue basic knowledge summary 5. Interview experience of byte beating Algorithm Engineer
  45. 【问题记录】- 谷歌浏览器 Html生成PDF
  46. [problem record] - PDF generated by Google browser HTML
  47. 【问题记录】- 谷歌浏览器 Html生成PDF
  48. [problem record] - PDF generated by Google browser HTML
  49. 【JavaScript】查漏补缺 —数组中reduce()方法
  50. [JavaScript] leak checking and defect filling - reduce() method in array
  51. 【重识 HTML (3),350道Java面试真题分享
  52. 【重识 HTML (2),Java并发编程必会的多线程你竟然还不会
  53. 【重识 HTML (1),二本Java小菜鸟4面字节跳动被秒成渣渣
  54. [re recognize HTML (3) and share 350 real Java interview questions
  55. [re recognize HTML (2). Multithreading is a must for Java Concurrent Programming. How dare you not
  56. [re recognize HTML (1), two Java rookies' 4-sided bytes beat and become slag in seconds
  57. 【重识 HTML ,nginx面试题阿里
  58. 【重识 HTML (4),ELK原来这么简单
  59. [re recognize HTML, nginx interview questions]
  60. [re recognize HTML (4). Elk is so simple