vue压缩base64图片方法 【Javascript】

	  //压缩方法
      dealImage(base64, w, callback) {
        var newImage = new Image();
        var quality = 0.6;    //压缩系数0-1之间
        newImage.src = base64;
        newImage.setAttribute("crossOrigin", 'Anonymous');	//url为外域时需要
        var imgWidth, imgHeight;
        newImage.onload = function () {
            imgWidth = 160;
            imgHeight = 90;
            var canvas = document.createElement("canvas");
            var ctx = canvas.getContext("2d");
            if (Math.max(imgWidth, imgHeight) > w) {
                if (imgWidth > imgHeight) {
                    canvas.width = w;
                    canvas.height = w * imgHeight / imgWidth;
                } else {
                    canvas.height = w;
                    canvas.width = w * imgWidth / imgHeight;
                }
            } else {
                canvas.width = imgWidth;
                canvas.height = imgHeight;
                quality = 0.6;
            }
            ctx.clearRect(0, 0, canvas.width, canvas.height);
            ctx.drawImage(this, 0, 0, canvas.width, canvas.height);
            var base64 = canvas.toDataURL("image/jpeg", quality); //压缩语句
            // 如想确保图片压缩到自己想要的尺寸,如要求在50-150kb之间，请加以下语句，quality初始值根据情况自定
            // while (base64.length / 1024 > 150) {
            // 	quality -= 0.01;
            // 	base64 = canvas.toDataURL("image/jpeg", quality);
            // }
            // 防止最后一次压缩低于最低尺寸，只要quality递减合理，无需考虑
            // while (base64.length / 1024 < 50) {
            // 	quality += 0.001;
            // 	base64 = canvas.toDataURL("image/jpeg", quality);
            // }
            callback(base64);//必须通过回调函数返回，否则无法及时拿到该值，return拿不到
        }
      }

　　

	  // 调用方法
	  let base64 = res.data; //传入base64变量
      console.log(base64.length, '11',base64); // 打印原长度
      vm.dealImage(base64, 150, useImg);
      function useImg(data){
        vm.formValidate.img = data
        console.log(vm.formValidate.img.length, '22',vm.formValidate.img); // 打印压缩长度
      }