base64和File之间转换

base64转成File

dataURLtoFile = (dataurl, filename) => {
        let arr = dataurl.split(',');
        let mime = arr[0].match(/:(.*?);/)[1];
        let bstr = atob(arr[1]);
        let n = bstr.length; 
        let u8arr = new Uint8Array(n);
        while(n--){
            u8arr[n] = bstr.charCodeAt(n);
        }
        //转换成file对象
        return new File([u8arr], filename, {type:mime});
        //转换成成blob对象
        //return new Blob([u8arr],{type:mime});
}

注释：atob()函数对已经使用base-64编码的数据字符串进行解码

File转成base64

getImgToBase64 = (url,callback) => {
    let 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);
      let dataURL = canvas.toDataURL('image/png');
      callback(dataURL);
      canvas = null;
    };
    img.src = url;
}