JS Base64转Blob上传示例 - JavaScript学习网

Base64 转 Blob 上传原理

例如，使用某些图片裁剪插件处理后，得到的图片数据通常以 Base64 格式呈现。


<img src="data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAEAAAAkCAYAAABIdFAMAAAAGXRFWHRTb2Z0d2FyZQBBZG9iZSBJbWFnZVJlYWR5ccllPAAAAHhJREFUeNo8zjsOxCAMBFB/　KEAUFFR0Cbng3nQPw68ArZdAlOZppPFIBhH5EAB8b+Tlt9MYQ6i1BuqFaq1CKSVcxZ2Acs6406KUgpt5/　LCKuVgz5BDCSb13ZO99ZOdcZGvt4mJjzMVKqcha68iIePB86GAiOv8CDADlIUQBs7MD3wAAAABJRU5ErkJggg==">

这种格式的数据如何直接在 form 表单中上传？虽然大多数裁剪插件已内置上传功能，但了解其底层原理仍具参考价值。

首先，需要将 Base64 数据流转换为 Blob 对象，因为文件对象通常继承自 Blob。

具体的转换函数实现如下。


function getBlobBydataURI(dataURI,type) { 
  var binary = atob(dataURI.split(',')[1]); 
  var array = []; 
  for(var i = 0; i < binary.length; i++) { 
    array.push(binary.charCodeAt(i)); 
  } 
  return new Blob([new Uint8Array(array)], {type:type }); 
}

完成转换后，剩余的操作即可按照常规文件上传流程进行。


var $Blob= getBlobBydataURI(base64Data,'image/png'); 
var formData = new FormData(); 
formData.append("files", $Blob ,"file_"+Date.parse(new Date())+".png");

完整的代码示例如下所示。


<!DOCTYPE html> 
<html> 
<head> 
  <meta http-equiv="Content-Type" content="text/html; charset=utf-8"/> 
  <title>上传用例</title> 
  <meta content='width=device-width, initial-scale=1, maximum-scale=1, user-scalable=no' name='viewport'> 
  <script type="text/javascript"> 
    /** 
     * 根据base64 内容 取得 bolb 
     * 
     * @param dataURI 
     * @returns Blob 
     */ 
    function getBlobBydataURI(dataURI,type) { 
      var binary = atob(dataURI.split(',')[1]); 
      var array = []; 
      for(var i = 0; i < binary.length; i++) { 
        array.push(binary.charCodeAt(i)); 
      } 
      return new Blob([new Uint8Array(array)], {type:type }); 
    } 
    /** 
     * 上传 
     */ 
    function upload(){ 
      //base64 转 blob 
      var $Blob= getBlobBydataURI(document.getElementsByTagName("img")[0].currentSrc,'image/jpeg'); 
      var formData = new FormData(); 
      formData.append("files", $Blob ,"file_"+Date.parse(new Date())+".jpeg"); 
      //组建XMLHttpRequest 上传文件 
      var request = new XMLHttpRequest(); 
      //上传连接地址 
      request.open("POST", "www.xxx.com"); 
      request.onreadystatechange=function() 
      { 
        if (request.readyState==4) 
        { 
          if(request.status==200){ 
            console.log("上传成功"); 
          }else{ 
            console.log("上传失败,检查上传地址是否正确"); 
          } 
        } 
      } 
      request.send(formData); 
    } 
  </script> 
</head> 
<body> 
<button onclick="upload()">上传测试</button> 
<br /> 
上传的图片: 
<img src="data:image/jpeg;base64,/9j/4AAQSkZJRgABAQEAeAB4AAD/4QAiRXhpZgAATU0AKgAAAAgAAQESAAMAAAABAAEAAAAAAAD/2wBDABsSFBcUERsXFhceHBsgKEIrKCUlKFE6PTBCYFVlZF9VXVtqeJmBanGQc1tdhbWGkJ6jq62rZ4C8ybqmx5moq6T/wAALCABQADEBAREA/8QAGgAAAwADAQAAAAAAAAAAAAAAAwQFAAECBv/EADQQAAIBAwMCAgcGBwAAAAAAAAECAwAEEQUSITFBE1EVImFxgaHwBiMykbHRFEJDcoKiwf/aAAgBAQAAPwD0tc5AGc1MuftBYW7FfEMrDtGM/Ohp9pbNmUNHOgbo7qAP1p60vra8z4E6uR1HcfCmVrKHc3EdrBJNI2FUZNSIreXWR41w7xW38kSnBYebe/686o2ljaWwPgQxqemRyT8aO8UTqVeJWHkQKlzaHDuaS0Y28/VSh9X3EeX17KNpWoPc+Lb3KBLiDhwOhHmKo5qPqY9Iajb6eM+Go8aX2jsK71dmhW2tIcxrcSCNivUKeuKnw2mnyXc1rbJcRzxAnxd/UijwajdXkVlbrIqSXCsXkA5wCRx7eDQ7i4i024KxXV3PMuGKytlD8vLP5UfUHCXunaimVEuEYDqQeRVmpthg61qjHqPDH+p/anL+0F1Eu1gskbB42Izhh0pA2mqSho3a1h38PLGvrMK3Ppj24tpbHBktl2hWON47/Hmg3FnPduxbThbyyDa0xlDBR34HsouvRCLSIYlOdjoo+FP+tU6+b0Zq63pH3E6iOU4/Cex+VWI5FkUMrAg9CO9BvEnlgZLaURy54YjOKniy1sHPpKM/4D9qqqWCgOctgZ46mpN4w1HWLe1TlLY+LIfb2FWKHPBHcxtHKgZWGCCKi2y3FnqbWdlJ40CgM6yf0xnoD9frV+sqPrt1eWsG6EbIzgNL3XnsPr/tOaXZQWduFhbfv9ZnPVj503trrApeG0hgllkiTa0xzIck5P0TTGKzFDmhjnieKRdyOMMOmayGJIYkijXaqDCjOcCi1ql5ruGGQRt4hcjdhI2fj4A1w2oQqMsJ1Hm1vIB+eKJLdRQuElbYCMh24X3Z86WXWLJtv3yDchfl14x2PPWmra4juYEmiIKsM9c49nvo9aqXdyPHf+LGWXbHsObeSQdc8YwPnS5vnvrdgk6uN2DttJOx8wTinJ3dZFmhuCrSIQscqHacc5x1HGaQWYiaFI2UoYWCsLSX8ORwBu5B8/3qrpxJs4zuRlx6hQEAr24PNN1qlXhlnkKykCDPCLzv/uPl7Pn2ocVm8UZKSBJd7MGAyCCxIBHfrW/4eaa4Es2xQIigCknDE8noOwFci0mjeAwyIPCgMW5lJycr2yPI96ZtIBbWscAbdsUDPnR6/9k=" /> 
</body> 
</html>

以上介绍了 JavaScript 中将 Base64 转换为文件上传的实例代码解析，希望对大家有所帮助。如有任何疑问，欢迎留言，小编会及时回复。感谢大家对本站的支持！

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