Answers for "how to decode base64 data url in javascript"

javascript base64 encode

var string = "Hello folks how are you doing today?";
var encodedString = btoa(string); // Base64 encode the String
var decodedString = atob(encodedString); // Base64 decode the String

Convert local url to base64 in javascript

var xhr = new XMLHttpRequest();       
    xhr.open("GET", "/path/to/local/image/file", true); 
    xhr.responseType = "blob";
    xhr.onload = function (e) {
            console.log(this.response);
            var reader = new FileReader();
            reader.onload = function(event) {
               var res = event.target.result;
               console.log(res)
            }
            var file = this.response;
            reader.readAsDataURL(file)
    };
    xhr.send()