canvas绘制圆图输出图片格式

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function drawCircleImage(url, callback) {          const canvas = document.createElement('canvas');          const img = new Image();          img.setAttribute("crossOrigin", 'Anonymous');          img.src = url;          img.onload = function() {              canvas.width = img.width;              canvas.height = img.height;              let ctx = canvas.getContext("2d");              //获取图片宽高的最小值              let min = Math.min(img.width, img.height);              let r = min / 2;              ctx.fillStyle = ctx.createPattern(img, 'no-repeat');              ctx.clearRect(0, 0, img.width, img.height);              ctx.arc(img.width / 2, img.height / 2, r, 0, Math.PI * 2);              ctx.fill(); 　　  let base64 = canvas.toDataURL("image/jpeg"); 　　  callback(base64); 　}; }