<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Title</title>
</head>
<body>
<input id="upload" type="file"/>
<script>
const FILETYPES = ["image/png", "image/jpg", "image/jpeg"]; // 受支持的文件类型
const MAX_FILESIZE = 1024 * 1024 * 3; // 1024 * 1024 为1M
const MAX_FILESIZESTRING = "3M"; // 文件大小字符
const COMPRESSRATIO = .5; // 压缩比例 0 - 1
const upload = document.querySelector("#upload");
const imageToBase64 = (file, callback) => {
const reader = new FileReader();
reader.readAsDataURL(file); // 文件转base64
reader.addEventListener("load", (e) => {
callback && callback(e.target.result);
});
};
const compress = (originalImage, compressRatio = 1, callback) => {
const image = new Image();
image.src = originalImage;
// document.body.appendChild(image); // 原图预览
/* 监听图片的load事件 */
image.addEventListener("load", function () {
let [sizeRatio, maxWidth, maxHeight] = [0, 1024, 1024]; // 图片压缩宽高比例和最大宽高
let [imageWidth, imageHeight] = [this.naturalWidth, this.naturalHeight]; // 图片实际宽高
let compressFlag = false; // 图片是否需要压缩
// 如果图片宽度大于最大宽度就等比压缩图片的高度
if (imageWidth > maxWidth) {
compressFlag = true;
sizeRatio = imageWidth / maxWidth;
maxHeight = imageHeight / sizeRatio;
}
// 如果图片高度大于最大高度就等比压缩图片的宽度
if (imageHeight > maxHeight) {
compressFlag = true;
sizeRatio = imageHeight / maxHeight;
maxWidth = imageWidth / sizeRatio;
}
// 如果不需要压缩
if (!compressFlag) {
maxWidth = imageWidth;
maxHeight = imageHeight;
}
// 使用canvas压缩图片
const canvas = document.createElement("canvas");
const ctx = canvas.getContext("2d");
canvas.setAttribute("id", "canvas");
canvas.width = maxWidth;
canvas.height = maxHeight;
// document.body.appendChild(canvas); // canvas预览
ctx.clearRect(0, 0, maxWidth, maxHeight); // 清除画布内所有像素
ctx.drawImage(image, 0, 0, maxWidth, maxHeight); // canvas绘制当前图片
const compressImage = canvas.toDataURL("image/jpeg", compressRatio); // 设置压缩类型和压缩比例获取压缩后的文件
callback && callback(compressImage);
});
}
upload.addEventListener("change", function (e) {
const [file] = e.target.files;
if (!file) this.value = ""; // file为空就阻止向下执行
const {type: fileType, size: fileSize} = file; // 获取文件类型和大小
// 检查是否支持的文件类型
if (!FILETYPES.includes(fileType)) {
this.value = "";
alert(`不支持${fileType}类型文件`);
return;
}
// 检查文件大小
if (fileSize > MAX_FILESIZE) {
this.value = "";
alert(`文件不能超过${MAX_FILESIZESTRING}`);
return;
}
imageToBase64(file, (originalImage) => {
compress(originalImage, COMPRESSRATIO, (compressImage) => {
const _img = new Image();
_img.src = compressImage;
const download = document.createElement("a");
download.href = compressImage;
download.innerText = "点击保存";
download.setAttribute("download", "demo.jpg");
document.body.appendChild(download);
document.body.appendChild(_img); // 压缩后的图片预览
});
});
})
</script>
</body>
</html>