js图片压缩

function canvasDataURL(path, obj, callback) {
  var img = new Image();
  img.src = path;
  img.onload = function () {
    var that = this;
    // 默认按比例压缩
    let w = that.width,
      h = that.height,
      scale = w / h;
    w = obj.width || w;
    h = obj.height || (w / scale);
    let quality = 0.7; // 默认图片质量为0.7
    //生成canvas
    let canvas = document.createElement('canvas');
    let ctx = canvas.getContext('2d');
    // 创建属性节点
    let anw = document.createAttribute("width");
    anw.nodeValue = w;
    let anh = document.createAttribute("height");
    anh.nodeValue = h;
    canvas.setAttributeNode(anw);
    canvas.setAttributeNode(anh);
    ctx.drawImage(that, 0, 0, w, h);
    // 图像质量
    if (obj.quality && obj.quality <= 1 && obj.quality > 0) {
      quality = obj.quality;
    }
    // quality值越小，所绘制出的图像越模糊
    let base64 = canvas.toDataURL('image/jpeg', quality);
    // 回调函数返回base64的值
    callback(base64);
  };
}

// 三个参数
// file：一个是文件(类型是图片格式)，
// config：一个是文件压缩的后宽度，宽度越小，字节越小{width,height,quality}
// callback：一个是容器或者回调函数
base64转Blob对象

 /**
* 将以base64的图片url数据转换为Blob
* @param urlData
*            用url方式表示的base64图片数据
*/
function convertBase64UrlToBlob(urlData) {
  var arr = urlData.split(','), mime = arr[0].match(/:(.*?);/)[1],
    bstr = atob(arr[1]), n = bstr.length, u8arr = new Uint8Array(n);
  while (n--) {
    u8arr[n] = bstr.charCodeAt(n);
  }
  return new Blob([u8arr], { type: mime });
}