在线图片转base64

  function ImgToBase64(url, callback, outputFormat) {  // outputFormat 用于指定输出格式的，遵循 MIME 标准
      var canvas = document.createElement('CANVAS'),
      ctx = canvas.getContext('2d'),
      img = new Image;
      img.crossOrigin = 'Anonymous';
      img.onload = function () {
        canvas.height = img.height;
        canvas.width = img.width;
        ctx.drawImage(img, 0, 0);
        const quality = 0. 7;  // 压缩的的关键所在，压缩比例
        var dataURL = canvas.toDataURL(outputFormat || 'image/jpeg'，quality );  // 指定输出格式的地方，遵循 MIME 标准
        callback.call(this, dataURL, img);
        canvas = null;
      };
      img.src = url;
    }
    // 调用函数
    ImgToBase64('http://7x2wdd.com2.z0.glb.qiniucdn.com/8eb43ae8fcbc01e130562908e6629bbe?imageMogr2/thumbnail/500%3E', function (base64, img) {
      // Base64DataURL
      img.src = base64;
      document.querySelector('#img').appendChild(img);
    });

• 如此便可以将图片以 base64 的形式展示出来了，至于之后是要保存还是怎么做就随你啦！
• 这里转自 ting_125的博客

转本地图片

    function convertImgToBase64(url, callback, outputFormat){
        var canvas = document.createElement('CANVAS');
        var ctx = canvas.getContext('2d');
        var img = new Image;
        img.crossOrigin = 'Anonymous';
        img.onload = function(){
          var width = img.width;
          var height = img.height;
          // 按比例压缩4倍
          var rate = (width<height ? width/height : height/width)/4;
          canvas.width = width*rate;
          canvas.height = height*rate;
          ctx.drawImage(img,0,0,width,height,0,0,width*rate,height*rate);
          var dataURL = canvas.toDataURL(outputFormat || 'image/png');
          callback.call(this, dataURL);
          canvas = null;
        };
        img.src = url;
      }

       function getObjectURL(file) {
            var url = null ;
            if (window.createObjectURL!=undefined) {  // basic
              url = window.createObjectURL(file) ;
            } else if (window.URL!=undefined) {       // mozilla(firefox)
              url = window.URL.createObjectURL(file) ;
            } else if (window.webkitURL!=undefined) { // web_kit or chrome
              url = window.webkitURL.createObjectURL(file) ;
            }
            return url ;
      }
     // 前端只需要给input file绑定这个change事件即可（上面两个方法不用管）huodong-msg为input class
      $('.huodong-msg').bind('change',function(event){
            var imageUrl = getObjectURL($(this)[0].files[0]);
            convertImgToBase64(imageUrl, function(base64Img){
              // base64Img为转好的base64,放在img src直接前台展示(<img src="data:image/jpg;base64,/9j/4QMZRXh...." />)
              alert(base64Img);
              // base64转图片不需要base64的前缀data:image/jpg;base64
              alert(base64Img.split(",")[1]);
            });
            event.preventDefault();
        });

• 此处转自按兵不动