Image convert to Base64

<input type="file" id="asd"/>

I would like to get the image in base64 once the user chose that (before submitting the form)

Something like :

$(input).on('change',function(){
  var data = $(this).val().base64file(); // it is not a plugin is just an example
  alert(data);
});

I read about File API and other stuffs, I would like a simple and cross-browsers solution (IE6/IE7 excluded obviously)

Any help appreciated thanks.

function readFile() {
  
  if (this.files && this.files[0]) {
    
    var FR= new FileReader();
    
    FR.addEventListener("load", function(e) {
      document.getElementById("img").src       = e.target.result;
      document.getElementById("b64").innerHTML = e.target.result;
    }); 
    
    FR.readAsDataURL( this.files[0] );
  }
  
}

document.getElementById("inp").addEventListener("change", readFile);

<input id="inp" type='file'>
<p id="b64"></p>
<img id="img" height="150">

_{(P.S: A base64 encoded image (String) 4/3 the size of the original image data)}

Check this answer for multiple images upload.

Browser support: http://caniuse.com/#search=file%20api
More info here: https://developer.mozilla.org/en-US/docs/Web/API/FileReader

Exactly what you need:) You can choose callback version or Promise version. Note that promises will work in IE only with Promise polyfill lib.You can put this code once on a page, and this function will appear in all your files.

The loadend event is fired when progress has stopped on the loading of a resource (e.g. after "error", "abort", or "load" have been dispatched)

Callback version

        File.prototype.convertToBase64 = function(callback){
                var reader = new FileReader();
                reader.onloadend = function (e) {
                    callback(e.target.result, e.target.error);
                };   
                reader.readAsDataURL(this);
        };

        $("#asd").on('change',function(){
          var selectedFile = this.files[0];
          selectedFile.convertToBase64(function(base64){
               alert(base64);
          }) 
        });

Promise version

    File.prototype.convertToBase64 = function(){
         return new Promise(function(resolve, reject) {
                var reader = new FileReader();
                reader.onloadend = function (e) {
                    resolve({
                      fileName: this.name,
                      result: e.target.result, 
                      error: e.target.error
                    });
                };   
                reader.readAsDataURL(this);
        }.bind(this)); 
    };

    FileList.prototype.convertAllToBase64 = function(regexp){
      // empty regexp if not set
      regexp = regexp || /.*/;
      //making array from FileList
      var filesArray = Array.prototype.slice.call(this);
      var base64PromisesArray = filesArray.
           filter(function(file){
             return (regexp).test(file.name)
           }).map(function(file){
             return file.convertToBase64();
           });
      return Promise.all(base64PromisesArray);
    };

    $("#asd").on('change',function(){
      //for one file
      var selectedFile = this.files[0];
      selectedFile.convertToBase64().
          then(function(obj){
            alert(obj.result);
          });
      });
      //for all files that have file extention png, jpeg, jpg, gif
      this.files.convertAllToBase64(/\.(png|jpeg|jpg|gif)$/i).then(function(objArray){
            objArray.forEach(function(obj, i){
                  console.log("result[" + obj.fileName + "][" + i + "] = " + obj.result);
            });
      });
    })

html

<input type="file" id="asd" multiple/>