我们经常需要获取图片的宽高,这需要在图片加载完成后才可以。
下面我就介绍几种判断图片是否加载完成的方法:
首先我们先写一个img标签
<img src="./img.png" alt="">
1.complete属性:
var imgNode = document.getElementsByTagName('img')[0];
var timer = setTimeout(function(){
if(imgNode.complete){
console.log('图片加载完成')
}
},20)
2.onload事件:
var imgNode = document.getElementsByTagName('img')[0];
imgNode.οnlοad=function(){
console.log('图片加载完成')
}
这里我就介绍这两种方式(兼容性好,推荐使用),像什么jq方法、readystatechange事件我就不介绍了。
这里我们来扩展一下,假如我们判断多张图片加载完成呢?
方法一、
var img = [];
var flag = 0;
var 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; //图片总数
for(var i = 0 ; i < imgTotal ; i++){
img[i] = new Image()
img[i].src = mulitImg[i]
img[i].onload = function(){
//document.getElementsByTagName('body')[0].appendChild(this)
// console.log(this.width)
flag++;
if( flag == imgTotal ){
console.log('图片全部加载完成')
}
}
}
方法二、通过Promise实现
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 = [];
let img = [];
let 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() {
resolve(this);
};
});
}
Promise.all(promiseAll).then(img => {
console.log(img); // [img, img, img, img]
});