ES6 新增的一些东西

2022-11-20 15:15:18

一、常量

不允许重复定义

 const a='HELLO'
 const a='world'//报错Uncaught SyntaxError: Identifier 'a' has already been declared
  const a='HELLO'
    a='world'//Uncaught TypeError: Assignment to constant variable.

二 let使用

  let:定义一个块级作用域的变量
    需要先定义再使用；(不存在变量提升)
    不能重复定义

普通变量(var 定义的)：

这叫做变量提升:先使用变量，然后在定义变量

 console.log(a);//不报错 undefined
     var a=100

相当于

var b;
console.log(b);b=100;
console.log(b)

let定义的(Es6新增)

不存在变量提升

  console.log(c);//报错:Uncaught ReferenceError: c is not defined
    let c=10;

let是一个块级作用域的变量：

        let c = 100;
        if(10> 9){
            let c=200;
            console.log(c);
        }
         console.log(c);
        // var  c = 300

结果:200,100

var 定义的话

 var  c = 100;
if(10> 9){
var  c=200;
 console.log(c);
}
onsole.log(c);

结果:200,200

  var i=10;
        var arr = [22,33,44,55]
        for(let i=0;i< arr.length;i++){

        }

        if(i>9){
            console.log(i+10);
        }

结果:20

三，js基本数据类型

 js的数据类型：
    string array number null undefined boolean object
    基本数据类型：string number null undefined boolean
    引用类型：array object
 const obj = {
            name: "谢小二",
            age: 22
        }
        var obj2 = obj;
        obj2.age = 90

        console.log(obj.age);

结果:90

基本数据类型引用只是引用了值，改变互不影响
a=10
b=a
b=20
a根本没变

而引用类型的引用引用的是内存地址，一个改变另一个也跟的改变，如上述代码

四  模板字符串

通过反引号来使用，字符串当中可以使用变量
    可以当作普通字符串来处理
    可以使用多行字符串
<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1">
    <title>Title</title>

</head>
<body>
<ul id="ul">

</ul>
</body>
 <script>
     var name='陈太章'
     console.log(`我的名字叫${name}`)

     document.getElementById('ul').innerHTML=`
      <li>赵俊明喜欢搞基</li>
      <li>肖博雅喜欢被搞</li>
      <li>路宁喜欢我给他戴帽子</li>
     `
    </script>
</html>

示例

五 解构变量

类型要一致，如果是对象的话字段名称要一致

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1">
    <title>Title</title>
    <script>
//        let [a,b,c,d]=[11,22,33,44];
//        console.log(a);//11
//        console.log(d);//44

//        let [a,b,c,[d]] = [89,90,99,[100]];
//        console.log(a);//89
//        console.log(c);//99
//        console.log(d);//100

        let obj={
            name:'aaa',
            sex:'male'
        }

        let {name,sex}=obj;
        console.log(name);//aaa
        console.log(sex);//male

    </script>
</head>
<body>

</body>
</html>

六对象的扩展

对象的扩展
    对象当中的属性可以简写
    对象当中的方法也可以简写
<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1">
    <title>Title</title>

    <script>
        var username = '长安大学';
        var addr = '陕西西安';

        function fun() {
            alert('it is very beautiful')
        }

        //注意字段要保持一致
        var obj = {
            username,
            addr,
            fun,
        };

        console.log(obj.username);
        obj.fun()

        //        var useranme = $("#text1").val();
        //        var password = $("#text2").val();

        //        $.get(url,{useranme,password},function(){
        //
        //
        //        })
    </script>
</head>
<body>

</body>
</html>

七、函数的扩展

函数的扩展
    可以给函数默认参数
    剩余参数：function fun(a,...b ){
    }
    fun(11,22,33)
    则：b = [22,33]

默认参数

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1">
    <title>Title</title>
    <script>
        function aa(name='渣渣辉') {
            console.log(name)
        }
        aa()
    </script>
</head>
<body>

</body>
</html>

剩余参数:

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1">
    <title>Title</title>
    <script>
//        function aa(name='渣渣辉') {
//            console.log(name)
//        }
//        aa()

        function bb(a,...b) {
            console.log(a);
            console.log(b);
        }

        bb('渣渣辉','古天乐','陈小春','贪玩蓝月')
    </script>
</head>
<body>

</body>
</html>

结果:

a=渣渣辉
b=["古天乐","陈小春","贪玩蓝月"]

八、数组的扩展

1)判断数组当中是否存在某个数值

indexOf  有就找出索引，没有则输出-1

 <script>
        aa=[11,22,33,44,55,66];
        console.log(aa.indexOf(55));//4
        console.log(aa.indexOf(45))//-1
    </script>

includes 有则显示true没有则显示false

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1">
    <title>Title</title>
    <script>
        aa=[11,22,33,44,55,66];
//        console.log(aa.indexOf(55));
//        console.log(aa.indexOf(45))

        console.log(aa.includes(55));//true
        console.log(aa.includes(45))//false
    </script>
</head>
<body>

</body>
</html>

2）对数组的遍历

aa=[11,22,33,44,55,66];
aa.forEach(function (item,index) {
            console.log(item,'----',index)
        })

3)map操作

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1">
    <title>Title</title>
    <script>
        aa=[11,22,33,44,55,66];
//        console.log(aa.indexOf(55));
//        console.log(aa.indexOf(45))
//
//        console.log(aa.includes(55));//true
//        console.log(aa.includes(45))//false

//
//        aa.forEach(function (item,index) {
//            console.log(item,'----',index)
//        })

        arr=aa.map(function (item,index) {
            return  item+1
        });
        console.log(arr)//[12,23,34,45,56,67]
    </script>
</head>
<body>

</body>
</html>

4)对数组的过滤

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1">
    <title>Title</title>
    <script>
        aa=[11,22,33,44,55,66];
//        console.log(aa.indexOf(55));
//        console.log(aa.indexOf(45))
//
//        console.log(aa.includes(55));//true
//        console.log(aa.includes(45))//false

//
//        aa.forEach(function (item,index) {
//            console.log(item,'----',index)
//        })

//        arr=aa.map(function (item,index) {
//            return  item+1
//        });
//        console.log(arr)//[12,23,34,45,56,67]

        arr1=aa.filter(function (item,index) {
            return item>50
        });

        console.log(arr1)//[55,56]
    </script>
</head>
<body>

</body>
</html>

九、类

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1">
    <title>Title</title>
    <script>
     Object.prototype.hobby='play game';
     function Person(name,age) {
         this.name=name;
         this.age=age;
         this.sayhello=function () {
             console.log('hello')
         }
     }
     Person.prototype.sayhello=function () {
         console.log('哈哈哈哈')
     };
     Person.prototype.addr='北京';
     var p=new Person('ctz',21);
     p.sayhello();
     console.log(p.addr);
     console.log(p.hobby)

    </script>
</head>
<body>

</body>
</html>
hello
北京
play game

大佬地址链接:

github:

https://github.com/ruanyf/es6tutorial/tree/gh-pages/docs

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