Appending Blob data

Is there a function for appending blob data in JavaScript I currently use the following approach:

var bb = new Blob(["Hello world, 2"], { type: "text/plain" });
bb = new Blob([bb, ",another data"], { type: "text/plain" });

And BlobBuilder function is not available in Chrome.



Blobs are "immutable" so you can't change one after making it. Constructing a new Blob that appends the data to an existing blob (as you wrote in your initial question) is a good solution.

If you don't need to use the Blob each time you append a part, you can just track an array of parts. Then you can continually append to the array and then construct the Blob at the end when you need it.

var MyBlobBuilder = function() { = [];

MyBlobBuilder.prototype.append = function(part) {;
  this.blob = undefined; // Invalidate the blob

MyBlobBuilder.prototype.getBlob = function() {
  if (!this.blob) {
    this.blob = new Blob(, { type: "text/plain" });
  return this.blob;

var myBlobBuilder = new MyBlobBuilder();

myBlobBuilder.append("Hello world, 2");

// Other stuff ... 

myBlobBuilder.append(",another data");
var bb = myBlobBuilder.getBlob();


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