直接上代码

function isLoadAll() {
   let arr = ['123.jpg', '456.png']
   let all_promis = [], item = null
   for (let i in arr) {
     all_promis[i] = new Promise((resolve, reject)=> {
        item = new Image()
        item.src = arr[i]
        item.onload = ()=> {
          resolve(item)
        }
     })
   }
   Promise.all(all_promis).then(()=> {
     console.log('图片全部加载完成...')
   })
}