Home > Article > Web Front-end > There are several ways to declare variables in es6
es6 There are 6 ways to declare variables: 1. Use the keyword var to declare variables; 2. Use the keyword function to declare variables; 3. Use the keyword const to declare variables; 4. Use the keyword let to declare variables; 5. Use the keyword class to declare variables; 6. Use the keyword import to declare variables.
The operating environment of this tutorial: Windows 7 system, ECMAScript version 6, Dell G3 computer.
ES5 has only two ways to declare variables: the var command and the function command.
ES6 In addition to adding let and const commands, there are two ways to declare variables: import command and class command.
So, ES6 has a total of 6 ways to declare variables.
1. Use the keyword var to declare variables
var a ; //undefined var b = 1;
2. Use the keyword function to declare the variable
function add(a) { var sum = a + 1; return sum; }
3. Declare the variable with the keyword const
const a; //报错,必须初始化 const b = 1;
must initializeconstants
4. Use the keyword let Declaring variables
let a; //undefined let b = 1; function add(b) { let sum = b + 1; return sum; } let c = add(b);
5. Use the keyword class to declare variables
Regarding class, I will write a separate article in detail later. To introduce, here is a brief introduction: First, look at the constructor in ES5, and then use ES6 classes to implement it:
// ES5写法 : function fun ( x, y ){ this.x = x; this.y = y; }; fun.prototype.GetHair = function(){ return `${this.x}掉了两根头发,${this.y}说俺也一样!`; }; let setHair = new fun('小明','老王'); console.log(setHair.GetHair()); // 小明掉了两根头发,老王说俺也一样!Let’s look at how ES6 classes are written:
class Interest { constructor( x, y, e, z ){ this.x = x; this.y = y; this.e = e; this.z = z; } MyInterest(){ let arr = []; console.log(`我会${[...arr,this.x,this.y,this.e,this.z]}!`); } } let GetInterest = new Interest('唱','跳','rap','篮球'); console.log(GetInterest.MyInterest()); //我会唱,跳,rap,篮球!ES6 classes can be regarded as just syntax sugar , most of its functions can be achieved by ES5. The new class writing method only makes the object prototype writing method clearer and more like the syntax of object-oriented programming. The constructor method is the construction method, and the this keyword represents the instance object. . That is, the constructor Point of ES5 corresponds to the constructor method of the Point class of ES6.
6. Use the keyword import to declare variables
import is used to load files. What is received in curly brackets is One or more variable names. These variable names need to be the same as the variable names you want to import.
举个栗子:你想要导入action.js文件中的某一个变量,这个变量里保存了一段代码块,所以你要写成:import { Button } from 'action'
,这个时候,你就从action.js中获取到了一个叫 Button 的变量,既然获取到了,你就可以对Button里的代码猥琐欲为了
如果想为输入的变量重新取一个名字,import
命令要使用as关键字,将输入的变量重命名,比如:
import { NewButton as Button } from 'action.js';
上面的代码表示从action.js文件中,获取一个变量名称叫做Button的代码段,然后你又声明了一个变量 NewButton ,将 Button 保存在 NewButton
【相关推荐:javascript视频教程、web前端】
The above is the detailed content of There are several ways to declare variables in es6. For more information, please follow other related articles on the PHP Chinese website!