js图片压缩

利用canvas 压缩图片大小

compressImage(base64, targSize = 60 * 1024) {
      return new Promise((resolve, reject) => {
        if (base64.length <= targSize) {
          resolve(base64);
          return;
        }
        var newImage = new Image();
        newImage.src = base64;
        console.log(base64.length);
        newImage.setAttribute("crossOrigin", "Anonymous"); //url为外域时需要
        newImage.onload = function() {
          var quality = 0.95; //压缩系数0-1之间
          var canvas = document.createElement("canvas");
          var ctx = canvas.getContext("2d");
          ctx.clearRect(0, 0, canvas.width, canvas.height);
          ctx.drawImage(this, 0, 0, canvas.width, canvas.height);
          var base64 = canvas.toDataURL("image/png", 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5-10kb之间，请加以下语句，quality初始值根据情况自定

          while (base64.length > targSize) {
            quality -= 0.05;
            base64 = canvas.toDataURL("image/png", quality);
          }
          resolve(base64);
        };
      });

效果：