Convert blob to base64

Question

var reader = new FileReader();
reader.readAsDataURL(blob); 
reader.onloadend = function() {
  var base64data = reader.result;                
  console.log(base64data);
}

Form the docs readAsDataURL encodes to base64

As an awaitable function:

function blobToBase64(blob) {
  return new Promise((resolve, _) => {
    const reader = new FileReader();
    reader.onloadend = () => resolve(reader.result);
    reader.readAsDataURL(blob);
  });
}

Note: The blob's result cannot be directly decoded as Base64 without first removing the Data-URL declaration preceding the Base64-encoded data. To retrieve only the Base64 encoded string, first remove data:/;base64, from the result.

this worked for me:

var blobToBase64 = function(blob, callback) {
    var reader = new FileReader();
    reader.onload = function() {
        var dataUrl = reader.result;
        var base64 = dataUrl.split(',')[1];
        callback(base64);
    };
    reader.readAsDataURL(blob);
};

There is a pure JavaSript way that is not depended on any stacks:

const blobToBase64 = blob => {
  const reader = new FileReader();
  reader.readAsDataURL(blob);
  return new Promise(resolve => {
    reader.onloadend = () => {
      resolve(reader.result);
    };
  });
};

For using this helper function you should set a callback, example:

blobToBase64(blobData).then(res => {
  // do what you wanna do
  console.log(res); // res is base64 now
});

---

I write this helper function for my problem on React Native project, I wanted to download an image and then store it as a cached image:

fetch(imageAddressAsStringValue)
  .then(res => res.blob())
  .then(blobToBase64)
  .then(finalResult => { 
    storeOnMyLocalDatabase(finalResult);
  });

var audioURL = window.URL.createObjectURL(blob);
audio.src = audioURL;

var reader = new window.FileReader();
reader.readAsDataURL(blob);
reader.onloadend = function () {
     base64data = reader.result;
     console.log(base64data);
}