canvas压缩图片

js压缩后台给的图片

arr是从后台接受数据的数组，定时器的作用是用来等图片加载完成（建议用complete属性来判断是否加载完成）。

 arr.forEach(function(item) {
          if (item.goods_photo) {
           
          let img = new Image();
            img.src = item.goods_photo;
             setTimeout(() => {
              let canvas = document.createElement("canvas")
                canvas.width = 200
                canvas.height = 200
                console.log(img)
                let context = canvas.getContext("2d")
                context.drawImage(img,0,0,200,200)
                let ress =canvas.toDataURL('image/jpeg', 1)
                item.main_photo_url = ress
                  // console.log(ress,8888888)
                 }, 3000);
          }
        });