前端图片预加载

// 图片 url 地址
let urls = ['url1', 'url2'];
let promiseAll = [];
let imgs = [];
const len = urls.length
for (let i = 0; i < len; i++） {
  promiseAll[i] = new Promise((res, rej) => {
    imgs[i] = new Image();
    imgs[i].src = urls[i];
    imgs[i].onload = () => {
        res(imgs[i]);
    }
  })
}
promise.all(promiseAll).then(img => {
    // 加载完成后的代码
    ···
})