Working plunkr for base64 String
https://plnkr.co/edit/PFfebmnqH0eQR9I92v0G?p=preview
handleFileSelect(evt){
var files = evt.target.files;
var file = files[0];
if (files && file) {
var reader = new FileReader();
reader.onload =this._handleReaderLoaded.bind(this);
reader.readAsBinaryString(file);
}
}
_handleReaderLoaded(readerEvt) {
var binaryString = readerEvt.target.result;
this.base64textString= btoa(binaryString);
console.log(btoa(binaryString));
}