JS event binding and event flow model case analysis

This time I will bring you a case analysis of JS event binding and event flow model. What are the precautions when using JS event binding and event flow model. The following is a practical case. Let’s take a look. .

1. JS events

(1) JS event classification

1. Mouse event :

click/dbclick/mouseover/mouseout

2. HTML event:

 onload/onunload/onsubmit/onresize/onchange/onfoucs/onscroll

3. Keyboard event:

keydown: triggered when the keyboard is pressed
keypress: when the keyboard is pressed and lifted Triggered instantly.
keyup: trigger when keyboard is raised

[Notes]

①Execution sequence: keydown keypress keyup
②keypress can only capture numbers, letters, and symbol keys, but not functions key.
③When long pressing, execute keydown--keypress in loop
④If there is keydown, there is not necessarily keyup. When the focus is lost when long pressing, keyup will no longer be triggered
⑤keypress is case-sensitive, keydown, kewup are not different.

4. Event factor:

When an event is triggered, the event will pass in a parameter by default to the function called by the event.

This parameter is a Event factors contain various detailed information of the event.

 document.onkeydown=function(e){
 console.log(e);
 }
document.onkeydown=function(){
console.log(window.event);
}

//兼容浏览器的写法：
document.onkeydown=function(e){
e==e||Window.event;
var Code=e.keyCode||e.which||e.charCode;
if(code==13){
//回车
}
}

5. How to determine the keyboard keys?

①In the re-starting function, receive the event factor e.
② You can use e.key to directly go to the pressed key character (not recommended).
③You can use keyCode/which/charCode to get the ASCII code value of the key.

(Compatible with writing methods of various browsers)

 var Code=e.keyCode||e.which||e.charCode;
//判断组合键
var isAlt=0,isEnt=0;
document.onkeyup=function(e){
if(e.keyCode==18){
isAlt=1;
}      
if(e.keyCode==13){
isEnt=1;
}    
if(isAlt==1&&isEnt==1){
alert("同时按下Alt和Enter键");
}
}
document.onkeyup=function(){
console.log("keyup");
}
document.onkeypress=function(){
console.log("keypress");
}
document.onkeydown=function(){
console.log("keydown");
}
document.onkeypress=function(){
console.log(window.event);
}
//判断是否按下了回车键
document.onkeydown=function(e){
var code=e.keyCode;
if(code==13){
alert("你输入的是回车键");
}
}

2. EventBinding model

(1) DOM0 event model

Notes on binding:

①Use window.onload to bind after loading is complete.

window.onload =function(){//Event}

②Place it behind the body for binding.

//body内容

  <button>内联模型绑定</button>
  <button>哈哈哈哈</button>
  <button>DOM2模型绑定</button>
  <button>取消DOM2</button>

1. Inline model (inline binding): Use the function name directly as the attribute value of the attribute in the html tag.

<button>内联模型绑定</button>

Disadvantages: It does not comply with the basic specifications of the w3c on the separation of content and behavior.

2. Script model (dynamic binding): Select a node in JS and then add the onclick attribute to the node.

document.getElementById("btn1")=function(){}

Advantages: It complies with the basic specifications of the w3c on the separation of content and behavior, and realizes the separation of html and js.
Disadvantages: The same type of event can only be added once to the same node. If added multiple times, the last one will take effect.

document.getElementById("btn1").onclick=function(){
  alert(1234);  
}
document.getElementById("btn1").onclick=function(){
  alert(234);  
}//重复的只能出现最近的一次

3.DOM0 has a common shortcoming: events bound through DOM0 cannot be canceled once bound.

document.getElementById("btn3").onclick=function(){//不能取消匿名函数
  if(btn.detachEvent){
    btn.detachEvent("onclick",func1);
  }else{
    btn.removeEventListener("click",func1);
  }
    alert("取消DOM2");
}

(2) DOM2 event model

1. Add DOM2 event binding:

①Before IE8, use .attachEvent("onclick", function);
②After IE8, use .addEventListener("click", function, true/false);
Parameter three: false (default) means event bubbling, passing in true means event capture.
③ Compatible with all browser processing methods:

 var btn=document.getElementById("btn1");
 if(btn.attachEvent){
 btn.attachEvent("onclick",func1);//事件，事件需要执行的函数IE8可以
 }else{
 btn.attachEventListener("click",func1);
 }

2. Advantages of DOM2 binding:

① The same node can be bound to multiple events of the same type using DOM2.
②Events bound using DOM2 can be canceled with special functions.
3. Cancel event binding:
① Use attachEvent to bind and use detachevent to cancel.
②Use attachEventListener to bind and use removeEventListenter to cancel.
Note: If the event bound to DOM2 needs to be canceled, when binding the event, the callback function must be a function name,
and cannot be an anonymous function, because when the event is canceled, the callback function Enter the function name to cancel.

3. JS event flow model

(1) Event flow model in JS

1. 事件冒泡(fasle/不写)：当触发一个节点的事件是，会从当前节点开始，依次触发其祖先节点的同类型事件，直到DOM根节点。
2. 事件捕获(true)：当初发一个节点的事件时，会从DOM根节点开始，依次触发其祖先节点的同类型事件，直到当前节点自身。
3. 什么时候事件冒泡？什么时候事件捕获？
 ① 当使用addEventListener绑定事件，第三个参数传为true时表示事件捕获；
 ② 除此之外的所有事件绑定均为事件冒泡。

4. 阻止事件冒泡：

 ① IE10之前，e.cancelBubble = true;
 ② IE10之后，e.stopPropagation();

5. 阻止默认事件：

 ① IE10之前：e.returnValue = false;
 ② IE10之后：e.preventDefault();

//css
#p1{
  width: 300px;;
  height: 300px;
  background-color: powderblue;
}
#p2{
  width: 200px;
  height: 200px;
  background-color: deeppink;
}
#p3{
  width: 100px;
  height: 100px;
  background-color:#A9A9A9;
}
//html
<p>
  </p><p>
    </p><p></p>
  

<a>超链接</a>
p1.addEventListener("click",function(){
  console.log("p1 click");
},false);
p2.addEventListener("click",function(){
  console.log("p2 click");
},false);
p3.addEventListener("click",function(){ //原来的顺序是：3-->2-->1。
//  myParagraphEventHandler(); //截获事件流后，只触发3.但是从2开始依然会冒泡；
  console.log("p3 click");
},false);

结果（事件冒泡）（由小到大p3-》p2-》p1）：

p1.addEventListener("click",function(){
  console.log("p1 click");
},true);
p2.addEventListener("click",function(){
  console.log("p2 click");
},true);
p3.addEventListener("click",function(){ 
//  myParagraphEventHandler(); //截获事件流后，只触发3.但是从2开始依然会冒泡；
  console.log("p3 click");
},true);

结果(事件捕获)（由小到大p3-》p2-》p1）：

//依然遵循事件冒泡
document.onclick=function(){
  console.log("document click")
}
//截获事件流阻止事件冒泡
function myParagraphEventHandler(e) {
   e = e || window.event;
  if (e.stopPropagation) {
     e.stopPropagation(); //IE10以后 
  } else {
     e.cancelBubble = true; //IE10之前
   }
}
//截获事件流阻止事件冒泡
function myParagraphEventHandler(e) {
   e = e || window.event;
  if (e.stopPropagation) {
     e.stopPropagation(); //IE10以后 
  } else {
     e.cancelBubble = true; //IE10之前
   }
}
//阻止默认事件
function eventHandler(e) {
  e = e || window.event;
// 防止默认行为 
   if (e.preventDefault) {
     e.preventDefault(); //IE10之后
  } else {
     e.returnValue = false; //IE10之前  
  }
}

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