ES6的模块化/class/promise及其他新的特性

class MathHandle {
    constructor(x, y) {
        this.x = x
        this.y = y
    }
    add() {
        return this.x + this.y
    }
}

const m = new MathHandle(1, 2)

console.log(typeof MathHandle)  // ‘function‘
console.log(MathHandle.prototype.constructor === MathHandle)  // true
console.log(m.__proto__ === MathHandle.prototype)  // true

function loadImg(src) {
    var promise = new Promise(function (resolve, reject) {
        var img = document.createElement(‘img‘)
        img.onload = function () {
            resolve(img)
        }
        img.onerror = function () {
            reject(‘图片加载失败‘)
        }
        img.src = src
    })
    return promise
}