<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8" />
</head>
<body>
<input type="file" id="upload" />
<script>
const ACCEPT = ["image/jpg", "image/png", "image/jpeg"];
const MAXSIZE = 3 * 1024 * 1024;
const MAXSIZE_STR = "3MB";
function convertImageToBase64(file, callback) {
let reader = new FileReader();
reader.addEventListener("load", function (e) {
const base64Image = e.target.result;
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;
let needCompress = false;
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 = "hidden";
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);
canvas.remove();
});
image.src = base64Image;
}
function uploadToServer(compressImage) {
console.log("upload to server...", compressImage);
}
const upload = document.getElementById("upload");
upload.addEventListener("change", function (e) {
const [file] = e.target.files;
if (!file) {
return;
}
const { type: fileType, size: fileSize } = file;
if (!ACCEPT.includes(fileType)) {
alert(`不支持[${fileType}]文件类型！`);
upload.value = "";
return;
}
if (fileSize > MAXSIZE) {
alert(`文件超出${MAXSIZE_STR}！`);
upload.value = "";
return;
}
convertImageToBase64(file, (base64Image) =>
compress(base64Image, uploadToServer)
);
});
</script>
</body>
</html>
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