Bottom Line: Here’s how to make an attractive file upload button for Bootstrap.

I put a lot of work into the new version of icsConverterWebapp. Here’s how my file upload buttons turned out:

My Bootstrap file upload button

See it live.

I’ve been learning to use Bootstrap for a few Flask projects I’ve been working on lately. I was surprised to see that the default Bootstrap file upload buttons are pretty ugly:

Default Bootstrap file upload button

To cut to the chase, I did tons of Googling, and this is the most satisfying solution I came up with. It is a combination of this popular solution by Cory LaViska, and this stackoverflow answer by Kirill Fuchs.

Further, I’m using Flask with wtforms, Flask-wtf, and Flask-bootstrap, so my solution uses code from all of these. If you’re not using these, skip to the bottom for a HTML and JS solution, and a link to a demo.

The basic idea is this:

  1. Use a basic file input element in a WTF form (the input element is ugly).
  2. Add a pretty Bootstrap label (basically a clickable descriptive item for a button) as an input-group-addon to the input.
  3. Hide the input, leaving only the pretty label.
  4. Add a place to display the uploaded filename for user feedback.
  5. Use some javascript to display the filename once uploaded (for user feedback).
  6. Add just a touch of CSS.

#1 — 4

Relevant part of index.html (a Jinja2 template)

{% block content %}
<div class="row">
    <form class="form-inline center-block" action="/" method="POST" enctype="multipart/form-data">
        {{ form.hidden_tag() }}
        <div class="input-group">
            <label id="browsebutton" class="btn btn-default input-group-addon" for="my-file-selector">
                {{ form.input_file(id="my-file-selector") }}
            <input type="text" class="form-control" readonly>
        {{ form.submit(class_="btn btn-primary") }}
{% endblock %}
{% block scripts %}
{{ super() }}
<script src="{{ url_for('.static', filename='js/inputFileButton.js') }}" ></script>
{% endblock %}

Note that the pretty label is for the ID of the (ugly) input button.

Relevant part of

from forms import UploadForm
from flask import request

@app.route('/', methods=['GET', 'POST'])
def index():
    form = UploadForm()
        if request.method == 'POST' and form.validate_on_submit():
            input_file = request.files['input_file']
            # Do stuff
            return render_template('index.html', form=form)

Not a whole lot of surprises here, a GET request returns the form, a POST to the same URL gets the uploaded file for processing.

from flask_wtf import Form
from flask_wtf.file import FileField, FileAllowed, FileRequired
from wtforms import SubmitField

class UploadForm(Form):

    validators = [
        FileRequired(message='There was no file!'),
        FileAllowed(['txt'], message='Must be a txt file!')

    input_file = FileField('', validators=validators)
    submit = SubmitField(label="Upload")


And inputFileButton.js (taken directly from Cory LaViska at the link above):

$(document).on('change', '#browsebutton :file', function() {
    var input = $(this),
        numFiles = input.get(0).files ? input.get(0).files.length : 1,
        label = input.val().replace(/\\/g, '/').replace(/.*\//, '');
    input.trigger('fileselect', [numFiles, label]);

$(document).ready( function() {
    $('#browsebutton :file').on('fileselect', function(event, numFiles, label) {
        var input = $(this).parents('.input-group').find(':text'),
            log = numFiles &gt; 1 ? numFiles + ' files selected' : label;

        if( input.length ) {
        } else {
            if( log ) alert(log);



Now we just use some CSS (SCSS in my case) to hide the ugly input button and give its new Browse... button the nice white color of Bootstrap’s btn-default in style.css:

#browsebutton {
    background-color: white;

#my-file-selector {
    display: none;

That’s all there is to it! I found Bootply really helpful in getting this all figured out. For those of you not using Flask, below is a simplified version using just Bootstrap, HTML, and the same JS as above, and here’s a link to a runnable demo at Bootply.

<form class="form-inline center-block" action="/" method="POST" enctype="multipart/form-data">
    <div class="input-group">
        <label id="browsebutton" class="btn btn-default input-group-addon" for="my-file-selector" style="background-color:white">
            <input id="my-file-selector" type="file" style="display:none;">
        <input type="text" class="form-control" readonly="">
    <button type="submit" class="btn btn-primary">Convert</button>