Image Preview With Carrierwave And Rails

Sep 30th, 2015
1 min read

Note: this assumes you already have carrierwave up and running. For help with that see the documentation on the carrierwave repo.

The other day I implemented image preview using Carrierwave and I couldn’t seem to find any great tutorials/blog posts on how to do it. Wanted to post how to do it in case someone else was interesting image preview as well.

# ... rest of the form ...

# Your carrierwave image uploader
<div class="form-group">
  <img id="img_prev" width=300 height=300 src="#" alt="your image" class="img-thumbnail hidden"/> <br/>
  <span class="btn btn-default btn-file">
    Upload Avatar Image<%= f.file_field :avatar, id: "avatar-upload" %>
  <%= f.hidden_field :avatar_cache %>

This is the javascript that will create an event handler on change for the file uploading input tag and display the image on the screen. I applied some basic bootstrap classes to the previewed image to make it look nicer.

$(function() {
  function readURL(input) {
    if (input.files && input.files[0]) {
      var reader = new FileReader();

      reader.onload = function (e) {


For more neat Rails Tips & Tricks check out my repo on github.


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