promise实现图片异步加载
Sunny-117 opened this issue · comments
promise实现图片异步加载
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8" />
<meta http-equiv="X-UA-Compatible" content="IE=edge" />
<meta name="viewport" content="width=device-width, initial-scale=1.0" />
<title>Document</title>
</head>
<style>
h1 {
display: block;
}
</style>
<body>
<div id="box">
<h1>我是一张缺省图</h1>
</div>
</body>
</html>
<style></style>
<script>
var oBox = document.getElementById("box");
var oH = document.querySelector("h1");
function loadImageAsync(url) {
return new Promise(function (resolve, reject) {
var image = new Image();
image.onload = function () {
resolve(image);
};
image.onerror = function () {
reject(new Error("Could not load image at " + url));
};
image.src = url;
});
}
// 模拟一下异步加载图片
// 用setTimeoutm模拟ajax调用接口，获取接口返回的图片路径，然后传入函数中，函数中已经提前创建好了
// 图片标签。我们在.then的回调函数中自行决定插入div容器中做一些事，比如把缺省图隐藏掉
setTimeout(() => {
loadImageAsync(
"https://img2020.cnblogs.com/blog/2221918/202104/2221918-20210429012928150-1671892053.png"
).then((res) => {
oH.style.display = "none";
oBox.appendChild(res);
});
}, 1000);
</script>
function loadImgAsync(url) { let img = new Image(url); return new Promise((rs, rj) => { img.onload = () => { rs(); } img.onerror = () => { rj(); } img.src = url; }) }