[javascript] 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.

It's useful to work with Deferred Object in this case, and return promise:

function readImage(inputElement) {
    var deferred = $.Deferred();

    var files = inputElement.get(0).files;
    if (files && files[0]) {
        var fr= new FileReader();
        fr.onload = function(e) {
            deferred.resolve(e.target.result);
        };
        fr.readAsDataURL( files[0] );
    } else {
        deferred.resolve(undefined);
    }

    return deferred.promise();
}

And above function could be used in this way:

var inputElement = $("input[name=file]");
readImage(inputElement).done(function(base64Data){
    alert(base64Data);
});

Or in your case:

$(input).on('change',function(){
  readImage($(this)).done(function(base64Data){ alert(base64Data); });
});

Function convert image to base64 using jquery (you can convert to vanila js). Hope it help to you!

Usage: input is your nameId input has file image

<input type="file" id="asd"/>
<button onclick="proccessData()">Submit</button>

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.5.1/jquery.min.js"></script>
<script>

async function converImageToBase64(inputId) {
  let image = $('#'+inputId)[0]['files']

  if (image && image[0]) {
    const reader = new FileReader();

    return new Promise(resolve => {
      reader.onload = ev => {
        resolve(ev.target.result)
      }
      reader.readAsDataURL(image[0])
    })
  }
}

async function proccessData() {
  const image = await converImageToBase64('asd')
  console.log(image)
}

</script>

Example: converImageToBase64('yourFileInputId')

https://codepen.io/mariohandsome/pen/yLadmVb

<input type="file" onchange="getBaseUrl()">

function getBaseUrl ()  {
    var file = document.querySelector('input[type=file]')['files'][0];
    var reader = new FileReader();
    var baseString;
    reader.onloadend = function () {
        baseString = reader.result;
        console.log(baseString); 
    };
    reader.readAsDataURL(file);
}

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/>

// https://developer.mozilla.org/en-US/docs/Web/API/FileReader/readAsDataURL

/* Simple */
function previewImage( image, preview, string )
{

    var preview     = document.querySelector( preview );
    var fileImage   = image.files[0];

    var reader      = new FileReader();

    reader.addEventListener( "load", function() {

        preview.style.height    = "100";
        preview.title           = fileImage.name;

        // convert image file to base64 string
        preview.src             = reader.result;

        /* --- */

        document.querySelector( string ).value = reader.result;                    

    }, false );

    if ( fileImage )
    {
        reader.readAsDataURL( fileImage );
    }

}

document.querySelector( "#imageID" ).addEventListener( "change", function() {

    previewImage( this, "#imagePreviewID", "#imageStringID" );

} )
/* Simple || */

<form>

    File Upload: <input type="file" id="imageID" /><br />
    Preview: <img src="#" id="imagePreviewID" /><br />    
    String base64: <textarea id="imageStringID" rows="10" cols="50"></textarea>

</form>

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