1、文件转babase64

function getImgToBase64(url,callback){//将图片转换为Base64
  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);
    var dataURL = canvas.toDataURL('image/png');
    callback(dataURL);
    canvas = null;
  };
  img.src = url;
}

2、base64转换为file/blob对象

function Base64toFile(dataurl, filename) {//将base64转换为文件
        var arr = dataurl.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 File([u8arr], filename, {type:mime});//file
        ///return new Blob([u8arr], { type: mime });////blob
    }

3、base64转blob

/*2:转bob*/
/**
 * 将以base64的图片url数据转换为Blob
 * @param base64    用url方式表示的base64图片数据
 * @return blob     返回blob对象           
 */
function convertBase64UrlToBlob(base64){
    var type =base64.split(",")[0].match(/:(.*?);/)[1];//提取base64头的type如 'image/png'     
    var bytes=window.atob(base64.split(',')[1]);//去掉url的头，并转换为byte (atob:编码 btoa:解码)

    //处理异常,将ascii码小于0的转换为大于0 
    var ab = new ArrayBuffer(bytes.length);//通用的、固定长度(bytes.length)的原始二进制数据缓冲区对象
    var ia = new Uint8Array(ab);
    for (var i = 0; i < bytes.length; i++) {
        ia[i] = bytes.charCodeAt(i);
    }
    return new Blob( [ab] , {type :type});
}

3、Blob转base64

function blobToBase64(blob, callback) {
    let a = new FileReader();
    a.onload = function (e) { callback(e.target.result); }
    a.readAsDataURL(blob);
}