用菜鸟教程模拟的
菜鸟对应链接 https://www.runoob.com/try/try-cdnjs.php?filename=tryhtml5_canvas_tut_img
<!DOCTYPE html> <html> <head> <meta charset="utf-8"> <title>菜鸟教程(runoob.com)</title> </head> <body> <p>Image to use:</p> <img id="scream" src="img_the_scream.jpg" alt="The Scream" width="220" height="277"><p>Canvas:</p> <canvas id="myCanvas" width="250" height="300" style="border:1px solid #d3d3d3;"> 您的浏览器不支持 HTML5 canvas 标签。</canvas> <img id="screamaa" src="" alt="The Scream" width="220" height="277"> <input type="file" id="uploadFile" accept="image/*" /> <script> var imgff= function (base64){ var bili = 0.7; //压缩后的图片尺寸,0.7就是70% var img=new Image() img.src = base64 console.log("img.width", img.width,"height", img.height) img.onload = function() { var c=document.getElementById("myCanvas"); var ctx=c.getContext("2d"); //图片地址加载完后执行操作 var newWidth = img.width; //压缩后图片的宽度 var newHeight = img.height; //压缩后图片的高度 c.width = newWidth; //压缩图的宽度 c.height = newHeight; //压缩图的高度 ctx.drawImage(img, 0, 0, newWidth,newHeight); //压缩 把图片放到画布上 ctx.font="30px Arial"; ctx.fillStyle = "#ffffff"; //设置水印 ctx.fillText("你好", 40, 40); //选择水印位置 let newBase64 = c.toDataURL("image/jpeg", 0.7); console.log("dnewBase64",newBase64) var c=document.getElementById("screamaa"); c.src =newBase64 } } var eleUploadFile = document.getElementById('uploadFile'); eleUploadFile.addEventListener('change', function(event) { var file = event.target.files[0] || event.target.dataTransfer.files[0]; var reader = new FileReader(); reader.onload = function(e) { var base64 = e.target.result; // canvas压缩图片，并且回调显示 imgff(base64) } reader.readAsDataURL(file); }); </script> </body> </html>