Js algorithm

Realize the factorial

 function JX(num){
            var sum = 1;
            for(i=num; i>0; i--){ sum = sum*i }return sum
        }
        console.log(JX(4));
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Maximum minimum value

var max = arr[0];
        for(i=0; i<arr.length; i++){if(arr[i]>max){ max = arr[i]; }}console.log(max);
  / / math methods
  var max = arr[0];
        for(i=0; i<arr.length; i++){ max =Math.max(arr[i],max)
        }
        console.log(max)
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Encapsulation of Max

function Max(arr){
     var max = arguments[0];
     for (var i = 0; i < arguments.length; i++) {
          if (max < arguments[i]) {
          max = arguments[i]; }}return max;
    };
}

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Fibonacci numbers

var Fb = function(n) {
	if( n==1 || n == 2) {return 1
	}else{
		return Fb(n-2) + Fb ( n-1)}}function printFb(n){
	for( let i =1; i<=n ; i++){
		console.log(Fb(i))
	}
}

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The sorting

function num(a, b){{
		 return a - b
	 }}
	 var arr = [1.9.8.5.6.2.3.7.4.8.6.3.6.8.9]
	 console.log(arr.sort(num))
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Array to heavy

function chong(arr){
	for( i= 0, i<= arr.length,i++){
		for(j = i+1, i<= arr.length,j++){
			if(arr[i] == arr[j]){
				arr.splice(j,1)}}}return arr
}
/ / set methods
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Take an even number

        var temp = [];
        for(i=0; i<arr.length; i++){if(arr[i]%2= =0){ temp.push(arr[i]); }}console.log(temp);
      filter
      console.log(arr.filter(x= >(x%2= =0)))
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Inversion array

  console.log(arr.reverse());
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Copy the array

 var arr = [1.2.3.4.5];
    var b = arr.concat();
    console.log(b);
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Json objects are converted to and from strings

1. Json string —–> JSON object

• Use the json.parse () function

var jsonStr = '{"name":"zhangsan","age":23,"email":"[email protected]"}';
var json = JSON.parse(jsonStr);
console.log(json);// Output :Object {name: "zhangsan", age: 23, email: "[email protected]"}
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2. Json object ——> JSON Character string

• JSON.stringify()

   var json = {name: "zhangsan".age: 23.email: "[email protected]"};
    var jsonStr = JSON.stringify(json);
    console.log(jsonStr);/ / output: "{" name" : "zhangsan", "age" : 23, "email" : "[email protected]"}"
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String to array

1. parseint
2. number

Array station Huawei string

1. string—->array

• split

2. array—->string

• Join passes in the partition symbol
• tostring

Array methods

1. increase

• Push is added from the very back of the array
• Unshift is added from the front of the array
• Concat does not change the array structure

2. delete

• Pop is removed from the back
• Shift is removed from the front
• Splice (subscript, value)

3. change

• arr[index] = value
• Slice (startIndex, endIndex) does not alter the array structure and returns the truncated contents

4. check

• indexof
• arr[index]
• Charat (index)

String method

1. Slice segmentation
2. Indexof lookup
3. Concat concates multiple arrays

Encapsulate native Ajax requests

var xhr = new XMLHttpReaqust()
xhr.open('get', uel)
xhr.send()
a.onreadystatechange = function () {
            if (a.readyState === 4 && a.status == 200) {
                Parse () converts a string to a JSON object
                var reponse = JSON.parse(a.responseText);
                console.log(reponse)
            }
        }
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Jq encapsulation ajax

$.ajax({
            url:"https://douban.uieee.com/v2/movie/top250".type:"get".dataType:"jsonp".success:function(res){
                var subjects = res.subjects;
                var data = subjects[0];
                var img = data.images.small;
                var title = data.title;
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vue

 new Vue({
            el: '#app'.data: {
                msg: "hello world"
            },
            // Before creation
            beforeCreate() {
                var url = 'https://douban.uieee.com/v2/movie/top250';
                $.get(url,res= >{
                    console.log(res);
                },"jsonp")}})Copy the code

react

    componentDidMount(){
        var url = "https://douban.uieee.com/v2/movie/top250";
        $.ajax({
            url,
            type:"get".dataType:"jsonp".success: res= > {
                var subjects = res.subjects[0];
                var img = subjects.images.small;
                var title = subjects.title;
                this.setState(() = >{
                    return {
                        img,
                        title
                    }
        
                })
            }
        })
    }
}
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The visible area changes with background scrolling

  <style>
        body{
            height: 2000px;
            background: darksalmon;
        }
        .bg{
            width: 500px;
            height: 500px;
            margin: 100px auto;
            background: url('./pexels-photo-698319.jpeg');
            background-attachment:fixed;
        }
    </style>
</head>
<body>
    <div class="bg"></div>
</body>
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