The most systematic summary of the key points of JavaScript (excluding basic language syntax)

1, variable
1. You can use new Array ("1", "2"); to define an array.
2. You can clear variables by assigning null to them, such as:

//首先定义一个变量
var i1=10;
i1=null;
//此时的i1就被清除了

Be careful when defining variables in functions like this

funtion demo(){
     x=10;
}
//而此前的代码中都没有出现x，那么这里就是定义了x，在调用demo函数以后，x就是一个全局变量了。

2. Operators == and = ==

var i="5";
var j=5;
if(i==j) alert(""hello);
if(i===j) alert("world");

//The above code will only pop up hello after running, because the values ​​​​of i and j are equal, but the data types of i and j are not equal. So == only requires equal values, but === not only requires equal values ​​but also requires equal data types.

Three, exception capture

try{
     if() throw "";
}catch(err){
     alert(throw);
}

Four, event
onload web page loading event
onclick click event
onfocus cursor gathering event
onselect text box selection event
onmouseover mouse over event
onmouserout mouse out event

5, dom operation
1, introduction: When the web page is loaded, the browser will create the document object model of the page.

2. DOM operation HTML
1) js can change all HTML elements in the page
①Change the output stream: document.write(); will overwrite all the contents of the document! Use with caution!
② Obtain elements: document.getElementById();
document.getElementByClass();
document.getElementByTagName(); etc.

Among them, tagname and this may get many Method of each element, the obtained elements become an object array, arranged in order

document.getElementById("btn").addEventListener("click",function(){
  var x=document.getElementsByName("people");
  var y=x[2].value;
  alert(y);
  });

③Change the Html content: innerHTML;
④Change the attribute content: After obtaining the object.Attribute = "Attribute value" then Yes, you can also use the setAttribute() method: the first parameter is the attribute name, and the second parameter is the attribute value
document.getElementById("pid").setAttribute("class","pid2");

The method of obtaining attribute values ​​uses getAttribute();

alert(document.getElementById("name").getAttribute("name"));

Some methods of dom controlling html:

          1，设置属性：如var attr=document.getElementById("demo1");
                              attr.setAttribute("title","dhello");//设置属性
                              var st=attr.getAttribute("title");//得到属性

                              alert(st);


          2.得到子节点：
                         var child=document.getElementsByTagName("ul")[1].childNodes;
                         alert(child.length);


          3得到父节点： var parent=document.getElementsByTagName("li")[0].parentNode;
                          alert(parent.nodeName);

          4创建元素节点：   var body=document.body;
                         var inp=document.createElement("input");//创建一个input节点
                         inp.type="button";//节点类型
                         inp.value="ann";
                         body.appendChild(inp);//把新的子节点添加到指定节点。（添加到末尾 ）

          5创建文本节点


          6删除子节点：<p id="p1">
                         <p id="p1">这是一个段落。</p>
                         <p id="p2">这是另一个段落。</p>
                         </p>

                         var parent=document.getElementById("p1");//找到 id="p1" 的元素：

                         var child=document.getElementById("p1");//找到 id="p1" 的 <p> 元素：

                         parent.removeChild(child);//从父元素中删除子元素：


                         第二种方法：var child=document.getElementById("p1");
                                       child.parentNode.removeChild(child);


          7动态添加节点(课选择添加的位置)
                                       var p=document.getElementById("p");
                                       var node=document.getElementById("pid");
                                       var newnode=document.creatElement("p");
                                       p.inserBefore(newnode,node);
                                                      要添加的 在这之前的

2) js can change all HTML attributes in the page
< ;!DOCTYPE HTML>
100db36a723c770d327fc0aef2ce13b1
93f0f5c25f18dab9d176bd4f6de5d30e

 <title>hello world</title>

9c3bca370b5104690d9ef395f2c5f8d1
6c04bd5ca3fcae76e30b72ad730ca86d

 <a id="aid"/>
 <p id=pid>hello world!!</p>

3f1c4e4b6b16bbbd69b2ee476dc4f83a

 document.getElementById("aid").href="www.baidu.com";//改变属性值

2cacc6d41bbb37262a98f745aa00fbf0
36cc49f0c466276486e50c850b7e4956
73a6ac4ed44ffec12cee46588e518a5e

3) js can change all CSS styles in the page

document.getElementById("pid").style.backgrouneColor="red";

4) js can react to all events in the page

5) DOM object controls HTML

6. Event handle EventListener
Event handle is an action that triggers an event. For example, onclick is the handle when it is clicked.
Event handles can be added in js, which can reduce a lot of code.
For example, the following is the traditional event triggering method
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The event handle added in the js code is as follows: the processing function cannot add () brackets!
var x=document.getElementById("btn");
x.addEventListener("click",demo);//There are two parameters here, one is the handle of the event, and the latter is the function that handles the event

To delete a handle, use removeEventListener();

Seven, events
1. Event flow: The order in which events are accepted on the page. There are two orders, namely event bubbling (from inside to outside), event capture (from outside to inside).

2. Event processing:
1) HTML event processing: directly added to the HTML structure

<button onclick="demo()"><button>

2) DOM level 0 event processing: assign a function to an event handler Attribute

<button id="btn"></button>
<script>
var btn1=document.getElementById("btn");
btn1.onclick= function () {
    document.getElementById("pid").style.backgroundColor="red";
};     
</script>

//Level 0 event processing Clear event processing is very simple, just assign onclick to empty. When setting, the time of the object is set to null instead of the object!
btn1.onclick=null;

//When there are multiple handlers for the same event, the previous one will be cleared by the later event handler.

btn1.onclick= function () {
    document.getElementById("pid").style.backgroundColor="red";//被覆盖
};
btn1.onclick= function () {
    document.getElementById("pid").style.backgroundColor="blue";
};

3) DOM level 2 event processing:

 addEventListener("事件名"，“事件处理函数”，“true/false”)；

true: event capture
false: event bubbling
To clear event processing, use removeEventListener();

//dom Level 2 event handlers will not be overwritten but will be parsed and executed step by step.

4) IE event handler. (Used in versions less than or equal to IE8, similar to the use of addEventListener.)

Add an event attachEvent
Delete an event detachEvent

5) It can be different according to the browser version Write different codes

if(btn.addEventListener){

     btn.addEventListener();
}
else{

     btn.attachEventListener()
}

3. Event object: An object will be generated when a dom event is triggered.

Attributes of the event object:
1) type: get the event type

document.getElementById("btn").addEventListener("click",showType);
function showType(e){
     alert(e.type);
}

2) target: get the event target: where this event is triggered, that is, the object of this event is an html element What elements in.

document.getElementById("btn").addEventListener("click",showTarget);
function showTarget(e){
     alert(e.target);
}

3) stopPropagation(): Prevent event bubbling: the innermost element event is triggered, but after this event occurs, the event of the upper element containing this element will also be triggered! So sometimes we don't want this to happen, which will prevent event bubbling from happening.
event.stopPropagation();

4) preventDefault(): Prevent event default behavior
event.preventDefault();

//dom 0级事件处理
//  var btn1=document.getElementById("btn");
//  btn1.onclick= function () {
//      document.getElementById("pid").style.backgroundColor="red";
//  };
//
//   btn1.onclick=null;
////dom 2级事件处理,处理函数不能加（）括号符！
//

//var btn=document.getElementById("btn");
//btn.addEventListener("click",demo1);
//
//function demo1(){
//
//// alert("dom 2级事件处理！");
//
//   document.getElementById("pid").innerHTML="dom 2级事件处理！";
//}

//事件对象

//1.获取事件对象的类型

//document.getElementById("btn").addEventListener("click",showType);
//function showType(e){
//   alert(e.type);
//}

//2.获取事件对象的目标

//document.getElementById("btn").addEventListener("click",showTarget);
//function showTarget(e){
//   alert(e.target);
//}

八，内置对象
1.什么是对象：js中所有事物都是对象，例如字符串，数组，时间，数值，函数等，每个对象都会带有属性和方法；
2.创建对象：
1）使用new object创建
people=new objet();
people.name="krys";
people.age=20;
2）直接创建：
people={name:"krys",age:20,addres:"guangdong"};
3）使用函数创建

funtion people(name,age){
     this.name=name;this.age=age};
son=new people("jess",20);//然后创建一个对象

document.getElementById("btn").addEventListener("click",creat);
function people(name,age){
          this.name=name;
          this.age=age;
     }
 function creat(){
          var name1= document.getElementById("name").value;
          var age1=document.getElementById("age").value;
          son=new people(name1,age1);
          alert(son.name);
          alert(son.age);
          }

3.字符串对象：String：字符串可以使用双引号也可以使用单引号！

属性：length：str.length可得到字符串的长度、
 indexOf(),在字符串中查找字符串，并返回字符串所在的位置。

document.getElementById("btn").addEventListener("click",creat);
     function creat(){
          var name= document.getElementById("name").value;
          if(name.match("krys")){

              alert("r所在的位置是"+name.indexOf("r"));
          }else{
              alert("sorry~you didnt have rights!")
          }

          }

match(),在字符串中匹配字符串，如果字符串1在字符串中存在，则将字符串1打印出来，如果没有就返回NULL

document.getElementById("btn").addEventListener("click",creat);
     function creat(){
          var name= document.getElementById("name").value;
          if(name.match("krys")){
              alert(name);
          }else{
              alert("sorry~you didnt have rights!")
          }

          }

replace(a,b) a是要替换掉的原来的字符或字符串，b是新的字符或字符串

document.getElementById("btn").addEventListener("click",creat);
     function creat(){
          var name= document.getElementById("name").value;
          if(name.match("krys")){

              alert(name.replace("krys","krys小仙女"));
          }else{
              alert("sorry~you didnt have rights!")
          }

          }

toUpperCase()转换成大写
 toLowerCase()转换成小写
 split()分隔线，将一个字符串分隔成若干部分，如str="hello,world,welcome,to";var s=str.split(","); s[0]="hello";

4.Date对象
1）创建Date对象：
var date=new Date();
alert(date);
var h=date.getHours();//时
var m=date.getMinutes();//分
var s=date.getSeconds();//秒

2)获取具体年份：getFullYear（）；
3）获取毫秒数：getTime();
4)设置具体的日期：setFullYear();
5)获取星期：getDay();

6）设置每秒更新一次
setTimeout(function(){

 showTime();},1000);

//每秒调用一次showTime函数

5.数组对象：
1)数组的创建：var a=["1","krys","ok"];
 var a=new Array(); a[0]="hell0"; a[1]="world";
 var a=new Array("hello","world","welcome");
 2)数组常用的方法：
 concat()合并数组如 a=["krys"];b=["tal"];a.concat(b)=krystal;
 sort()排序数组 var a=["a","c","b"];a.sort();->a b c (默认从低到高排序)
 设置为降序：a.sort(funtion(a,b){return a-b;})
 push()在数组末尾添加一个元素var a=["a","c","b"]; a.push("d");
 reverse()翻转，对称中心点相互交换：a.reverse()= c b a ;

6.math对象
 1）常用函数
 round()四舍五入 Math.round(2.5)=3;
 random()返回0~1之间的随机数 Math.random();
 可以转换成整数：parseInt(Matn.random()*10);
 max()返回最大值
 min()返回最小值
 abs()返回绝对值

九，浏览器的内置对象BOM（browser object model）
1，window对象：大部分对象的祖先，最高级别对象之一。

1）简介：Window对象是指当前的浏览器窗口，所有的js全局变量函数以及变量都是Window对象的成员。
其中，全局变量是window对象的属性，全局函数是window对象的方法。

2）获得浏览器内部窗口的尺寸（即内容区域的尺寸，不包括滚动条工具栏等）：
window.innerHeight浏览器窗口的内部高度,window.innerWidth，浏览器的内部宽度。

3）使用window.open(url)可以打开一个窗口，使用window.close()可以关闭当前窗口。

2,history对象
window.history()对象包含浏览器的历史（url）的集合
有三个方法：
1）history.back()后退，返回到前一页
2）history.forward()，前进，进入到下一页
3)history.go()，带参数，参数就是要进入的页数，-1是前一页，-2是前两页，依次类推，当前页是0.

3, timer
By using js, execute the code after a set time interval instead of executing it immediately after the function is called
There are two functions
One is setInterval() -Continuously execute the specified code at an interval of the specified number of milliseconds
One is setTimeout()-execute the specified code after pausing for the specified number of milliseconds.
You can use setTimeout to implement the function of setInterval(): just call yourself in the calling function code!
setInterval(funtion(){},1000);
setTimeout(funtion(){},1000);

You can use clearInterval(), clearTimeout() to clear this call,

4, Location object
is used to obtain the address of the current page and redirect the browser to a new page (in fact, my understanding is to parse the current address)

Properties of the Location object:
location.hostname: Returns the domain name of the web host
location.pathname: Returns the path and file name of the current page
location.port: Returns the port of the web host
location.protocol: Returns the used web protocol
location.href: Returns the url of the current page
location.assign() loads a new document, and the parameter is the path of the document to be loaded.

window.location.hostname;

5, screen object
window.screen object contains information about the user's screen
screen.avaiilWidth;//Available screen height
screen.availHeight;//Available screen width
screen.height;//Screen height
screen.width;//Screen width

6, navigation object
7, pop-up window , cookie

ten, js object-oriented thinking

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