JavaScript 类存在吗？ [关闭]

Question

我知道 javascript 中不存在类。

但是，有没有间接的方式在 javascript 中创建一个类？

在javascript中定义一个类有什么用

Answer 1

在 ECMAScript 2015 中引入的 JavaScript 类主要是 JavaScript 现有的基于原型的继承的语法糖。类语法并未向 JavaScript 引入新的面向对象的继承模型。 JavaScript 类提供了一种更简单、更清晰的语法来创建对象和处理继承。

这里有两个使用 ES5 和 ES6 的例子

'use strict';

/**
 * Shape class.
 * 
 * @constructor
 * @param {String} id - The id.
 * @param {Number} x  - The x coordinate.
 * @param {Number} y  - The y coordinate.
 */
function Shape(id, x, y) {
    this.id = id;
    this.setLocation(x, y);
}

/**
 * Set shape location.
 * 
 * @param {Number} - The x coordinate.
 * @param {Number} - The y coordinate.
 */
Shape.prototype.setLocation = function(x, y) {
    this.x = x;
    this.y = y;
};

/**
 * Get shape location.
 * 
 * @return {Object}
 */
Shape.prototype.getLocation = function() {
    return {
        x: this.x,
        y: this.y
    };
};

/**
 * Get shape description.
 * 
 * @return {String}
 */
Shape.prototype.toString = function() {
    return 'Shape("' + this.id + '")';
};

/**
 * Circle class.
 * 
 * @constructor
 * @param {String} id     - The id.
 * @param {Number} x      - The x coordinate.
 * @param {Number} y      - The y coordinate.
 * @param {Number} radius - The radius.
 */
function Circle(id, x, y, radius) {
    Shape.call(this, id, x, y);
    this.radius = radius;
}
Circle.prototype = Object.create(Shape.prototype);
Circle.prototype.constructor = Circle;

/**
 * Get circle description.
 * 
 * @return {String}
 */
Circle.prototype.toString = function() {
    return 'Circle > ' + Shape.prototype.toString.call(this);
};

// test the classes
var myCircle = new Circle('mycircleid', 100, 200, 50); // create new instance
console.log(myCircle.toString()); // Circle > Shape("mycircleid")
console.log(myCircle.getLocation()); // { x: 100, y: 200 }

'use strict';

/**
 * Shape class.
 * 
 * @constructor
 * @param {String} id - The id.
 * @param {Number} x  - The x coordinate.
 * @param {Number} y  - The y coordinate.
 */
class Shape(id, x, y) {
    constructor(id, x, y) { // constructor syntactic sugar
        this.id = id;
        this.setLocation(x, y);
    }
    
    /**
     * Set shape location.
     * 
     * @param {Number} - The x coordinate.
     * @param {Number} - The y coordinate.
     */
    setLocation(x, y) { // prototype function
        this.x = x;
        this.y = y;
    }
    
    /**
     * Get shape location.
     * 
     * @return {Object}
     */
    getLocation() {
        return {
            x: this.x,
            y: this.y
        };
    }
    
    /**
     * Get shape description.
     * 
     * @return {String}
     */
    toString() {
        return `Shape("${this.id}")`;
    }
}

/**
 * Circle class.
 * 
 * @constructor
 * @param {String} id     - The id.
 * @param {Number} x      - The x coordinate.
 * @param {Number} y      - The y coordinate.
 * @param {Number} radius - The radius.
 */
function Circle extends Shape {
    constructor(id, x, y, radius) {
        super(id, x, y); // call Shape's constructor via super
        this.radius = radius;
    }
    
    /**
     * Get circle description.
     * 
     * @return {String}
     */
    toString() { // override Shape's toString
        return `Circle > ${super.toString()}`; // call `super` instead of `this` to access parent
    }
}

// test the classes
var myCircle = new Circle('mycircleid', 100, 200, 50); // create new instance
console.log(myCircle.toString()); // Circle > Shape("mycircleid")
console.log(myCircle.getLocation()); // { x: 100, y: 200 }

More details here

Answer 2

使用这个例子。

    class Rectangle {
  constructor(height, width) {
    this.height = height;
    this.width = width;
  }

  get area() {
    return this.calcArea();
  }

  calcArea() {
    return this.height * this.width;
  }
}

const square = new Rectangle(10, 10);

console.log(square.area);

所以基本上，你可以创建类，它们需要以“init”函数开始，该函数通常是构造函数。之后您可以添加尽可能多的功能。注意：以上代码来自：https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Classes