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canvas-compress.html
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canvas-compress.html
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<!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>canvas图片压缩</title>
</head>
<body>
<input type="file" id="upload" />
<script>
const ACCRPT = ["image/jpg", "image/png", "image/jpeg"]; // 支持的图片格式
const MAXSIZE = 1024 * 1024; // 最大尺寸 1M
const MAXSIZE_STR = "1MB";
const upload = document.getElementById("upload");
// 将图片转成base64
function converImageToBase64(file, callback) {
let reader = new FileReader();
reader.addEventListener("load", (e) => {
// console.log(e.target.result);
const base64Image = e.target.result;
callback && callback(base64Image);
reader = null;
});
reader.readAsDataURL(file);
}
/**
* 压缩算法
* 1、图片的尺寸 不能超过1024 * 1024
* 2、图片的分辨率 toDataURL
*/
function compress(base64Image, callback) {
// console.log(base64Image);
let maxW = 1024;
let maxH = 1024;
const image = new Image();
image.addEventListener("load", (e) => {
let ratio; // 图片压缩比
let needCompress = false; // 是否需要压缩
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;
}
// 如果不需要压缩,需要获取图片的实际尺寸
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 = "hidden"; // visible
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", 0.8);
// console.log(compressImage);
callback && callback(compressImage);
canvas.remove();
let _image = new Image();
_image.src = compressImage;
document.body.appendChild(_image);
console.log("压缩比:", image.src.length / _image.src.length);
});
image.src = base64Image;
document.body.appendChild(image);
}
// 将图片上传到服务器
function upLoadToServer(compressImage) {
console.log("upload to server...", compressImage);
}
upload.addEventListener("change", (e) => {
console.log(e.target.files);
const [file] = e.target.files;
if (!file) {
return;
}
const { type: fileType, size: fileSize } = file;
/**
* 文件类型校验
* 旧的判断写法:ACCRPT.indexOf(fileType) < 0
* 新写法 ACCRPT.includes(fileType)
*/
if (!ACCRPT.includes(fileType)) {
alert(`不支持[${fileType}]文件类型`);
upload.value = "";
return;
}
// 文件大小校验
if (fileSize > MAXSIZE) {
alert(`文件超出${MAXSIZE_STR}`);
upload.value = "";
return;
}
// 压缩图片
converImageToBase64(file, (base64Image) =>
compress(base64Image, upLoadToServer)
);
});
</script>
</body>
</html>