简单实现一下文件上传图片压缩
步骤
- 创建一个input标签，监听一下上传状态，获取文件类型和文件大小判断
- 利用
FileReader异步读取文件（结合input:file可以很方便的读取本地文件）readAsDataURL方法读取指定的 [File] 对象，监听一下load过程获取图片的base64编码。 - 设定图片最大长宽，压缩的图片。监听Image方法load事件获取图片长宽，计算压缩比，获取到压缩后的长宽，最后利用cancas重新绘制图片后转化为base64格式的url输出
具体代码如下：
<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>
<body>
<input type="file" id="upload" />
<script>
const upload = document.getElementById("upload");
const ACCEPT = ["image/jpg", "image/png", "image/jpeg"];
const MAXSIZE = 1024 * 1024;
function convetImageToBase64(file, callback) {
let reader = new FileReader();
reader.addEventListener("load", function (e) {
const base64Image = e.target.result;
// 压缩前的url的base64大小
console.log(base64Image);
callback && callback(base64Image);
reader = null;
});
reader.readAsDataURL(file);
}
function compress(base64Image, callback) {
let maxW = 1024;
let maxH = 1024;
const image = new Image();
image.addEventListener("load", function (e) {
let ratio; //图片的压缩比
let needCompress = false; //是否压缩
if (maxW < image.naturalWidth) {
needCompress = true;
ratio = image.naturalWidth / maxW;
maxH = image.naturalHeight / ratio;
}
if (maxH < image.naturalHeight) {
needCompress = true;
ratio = image.naturalHeight / maxH;
maxW = image.naturalWidth / ratio;
}
if (!needCompress) {
maxW = image.naturalWidth;
maxH = image.naturalHeight;
}
const canvas = document.createElement("canvas");
canvas.setAttribute("id", "__compress__");
canvas.width = maxW;
canvas.height = maxH;
canvas.style.visibility = "visibile";
document.body.appendChild(canvas);
const ctx = canvas.getContext("2d");
ctx.clearRect(0, 0, maxW, maxH);
ctx.drawImage(image, 0, 0, maxW, maxH);
const compressImage = canvas.toDataURL("image/jpeg", 0.9);
callback && callback(compressImage);
const _image = new Image();
_image.src = compressImage;
document.body.appendChild(_image);
canvas.remove();
});
image.src = base64Image;
document.body.appendChild(image);
}
function uploadToServer(compressImage) {
// "压缩后的url的base64格式"
console.log("上传", compressImage);
}
// 监听图片上传时的改变获取file
upload.addEventListener("change", (e) => {
const [file] = e.target.files;
if (!file) {
return;
}
const { type: fileType, size: fileSize } = file;
if (!ACCEPT.includes(fileType)) {
alert("不支持[" + fileType + "]类型");
upload.value = "";
return;
}
if (fileSize > MAXSIZE) {
alert(`文件超出1MB`);
}
//图片压缩
convetImageToBase64(file, (base64Image) =>
compress(base64Image, uploadToServer)
);
});
</script>
</body>
</html>
效果： 第一张图片是未压缩处理的第二张图片是压缩处理后
