學(xué)習(xí)自http://www.daqianduan.com/6419.html
單張圖片(圖片在文檔中)

// HTML
<img id='xiu' src=""> 
//js
 $(document).ready(function(){

    //jquery
    $('#xiu').load(function(){
       // 加載完成 
    });

   //原生  onload
    var xiu = document.getElementById('xiu')
    xiu.onload = xiu.onreadystatechange = function(){
       if(!this.readyState||this.readyState=='loaded'||this.readyState=='complete'){
           // 加載完成 
       }
    };

})

注：
1、IE8及以下版本不支持onload事件钻弄，但支持onreadystatechange事件佃却；
2、readyState是onreadystatechange事件的一個狀態(tài)窘俺，值為loaded或complete的時候饲帅，表示已經(jīng)加載完畢。
3瘤泪、以下內(nèi)容省略兼容

單張圖片(圖片動態(tài)創(chuàng)建)

//js
 var xiu = new Image()
 xiu.src = 'http://www.daqianduan.com/wp-content/uploads/2014/11/hs-xiu.jpg'
 xiu.onload = function(){
    // 加載完成 
 }

單張圖片(結(jié)合Promise)

//js
 new Promise((resolve, reject)=>{
    let xiu = new Image()
    xiu.src = 'http://www.daqianduan.com/wp-content/uploads/2014/11/hs-xiu.jpg'
    xiu.onload = function(){
       // 加載完成 
       resolve(xiu)
    }
 }).then((xiu)=>{
 //code
 })

多張圖片

var img = [],  
    flag = 0, 
    mulitImg = [
    'http://www.daqianduan.com/wp-content/uploads/2017/03/IMG_0119.jpg',
    'http://www.daqianduan.com/wp-content/uploads/2017/01/1.jpg',
    'http://www.daqianduan.com/wp-content/uploads/2015/11/jquery.jpg',
    'http://www.daqianduan.com/wp-content/uploads/2015/10/maid.jpg'
 ];
 var imgTotal = mulitImg.length;
 for(var i = 0 ; i < imgTotal ; i++){
    img[i] = new Image()
    img[i].src = mulitImg[i]
    img[i].onload = function(){
       //第i張圖片加載完成
       flag++
       if( flag == imgTotal ){
          //全部加載完成
       }
    }
 }

多張圖片(結(jié)合Promise)

  let mulitImg = [
     'http://www.daqianduan.com/wp-content/uploads/2017/03/IMG_0119.jpg',
     'http://www.daqianduan.com/wp-content/uploads/2017/01/1.jpg',
     'http://www.daqianduan.com/wp-content/uploads/2015/11/jquery.jpg',
     'http://www.daqianduan.com/wp-content/uploads/2015/10/maid.jpg'
 ];
 let promiseAll = [], img = [], imgTotal = mulitImg.length;
 for(let i = 0 ; i < imgTotal ; i++){
     promiseAll[i] = new Promise((resolve, reject)=>{
         img[i] = new Image()
         img[i].src = mulitImg[i]
         img[i].onload = function(){
              //第i張加載完成
              resolve(img[i])
         }
     })
 }
 Promise.all(promiseAll).then((img)=>{
     //全部加載完成
 })