如何用新的 Blob 构造函数替换已弃用的 BlobBuilder？

Question

由于 Blobbuilder 已被弃用，而且我最近决定使用新的面部识别 API，因此我很难切换到“blob”。

function dataURItoBlob(dataURI, callback) {
        // convert base64 to raw binary data held in a string
        // doesn't handle URLEncoded DataURIs

        var byteString;
        if (dataURI.split(',')[0].indexOf('base64') >= 0) {
            byteString = atob(dataURI.split(',')[1]);
        } else {
            byteString = unescape(dataURI.split(',')[1]);
        }

        // separate out the mime component
        var mimeString = dataURI.split(',')[0].split(':')[1].split(';')[0];

        // write the bytes of the string to an ArrayBuffer
        var ab = new ArrayBuffer(byteString.length);
        var ia = new Uint8Array(ab);
        for (var i = 0; i < byteString.length; i++) {
            ia[i] = byteString.charCodeAt(i);
        }

        // write the ArrayBuffer to a blob, and you're done
        var BlobBuilder = window.WebKitBlobBuilder || window.MozBlobBuilder;
        var bb = new BlobBuilder();
        bb.append(ab);
        return bb.getBlob(mimeString);
}

我尝试将其切换为：

        // write the ArrayBuffer to a blob, and you're done
        var Blob = window.URL || window.webkitURL;
        var bb = new Blob();

        /*var link = document.createElement('link');
        link.rel = 'stylesheet';
        link.href = window.URL.createObjectURL(blob);
        document.body.appendChild(link);*/

        /*var BlobBuilder = window.WebKitBlobBuilder || window.MozBlobBuilder;
        var bb = new BlobBuilder();
        bb.append(ab);*/
        return bb.getBlob(mimeString);
}

但我在控制台中不断收到Uncaught TypeError: Object #<URL> has no method 'getBlob'。不知道我错过了什么。如果我尝试使用bb.append(ab);，我会在控制台中得到Uncaught TypeError: Object #<Blob> has no method 'append'。

Answer 1

从BlobBuilder 切换到Blob 非常简单。尝试以下向后兼容的代码（catch 块中的内容是您的原始代码）：

...
    try {
        return new Blob([ab], {type: mimeString});
    } catch (e) {
        // The BlobBuilder API has been deprecated in favour of Blob, but older
        // browsers don't know about the Blob constructor
        // IE10 also supports BlobBuilder, but since the `Blob` constructor
        //  also works, there's no need to add `MSBlobBuilder`.
        var BlobBuilder = window.WebKitBlobBuilder || window.MozBlobBuilder;
        var bb = new BlobBuilder();
        bb.append(ab);
        return bb.getBlob(mimeString);
    }
}

Answer 2

Blob = (function() {
  var nativeBlob = Blob;

  // Add unprefixed slice() method.
  if (Blob.prototype.webkitSlice) {
    Blob.prototype.slice = Blob.prototype.webkitSlice;  
  }
  else if (Blob.prototype.mozSlice) {
    Blob.prototype.slice = Blob.prototype.mozSlice;  
  }

  // Temporarily replace Blob() constructor with one that checks support.
  return function(parts, properties) {
    try {
      // Restore native Blob() constructor, so this check is only evaluated once.
      Blob = nativeBlob;
      return new Blob(parts || [], properties || {});
    }
    catch (e) {
      // If construction fails provide one that uses BlobBuilder.
      Blob = function (parts, properties) {
        var bb = new (WebKitBlobBuilder || MozBlobBuilder), i;
        for (i in parts) {
          bb.append(parts[i]);
        }
        return bb.getBlob(properties && properties.type ? properties.type : undefined);
      };
    }        
  };
}());

在您打算使用 Blob 之前将其包含在内，您将能够在仅支持已弃用的 BlobBuilder 的浏览器中使用 Blob 构造函数。