[JAVA] Image preview function


When posting an image, I felt that it was difficult to understand because only the name of the image file was displayed, so I implemented a preview function.

** Before implementing preview function **

1. Preparation

** 1. Create a js file to implement the preview function. Create preview.js in app/javascript/packs ** → app / javascript / packs / preview.js

** 2. Edit application.js so that preview.js can be loaded. ** **


require('./preview') #Append

** 3. Specify where the image will be displayed in the view file. ** **


<div class="img-upload">
  <div class="left-img-upload">
    <div class="weight-bold-text">
Related images(Please attach any related images)
    <div class="click-upload">
      <p>Click to upload file</p>
      <%= f.file_field :image, id:"idea-image" %>
  <div class="right-img-upload">
    <div id="image"></div>  <!--Append-->

2. Implementation of preview function

** Write the preview function code in preview.js created in 1. ** **


if (document.URL.match( /new/ ) || document.URL.match( /edit/ )) {
  document.addEventListener('DOMContentLoaded', function(){
    const ImageList = document.getElementById('image');

    const createImageHTML = (blob) => {
       //Generate a div element to display an image
      const imageElement = document.createElement('div');
      //Generate an image to display
      const blobImage = document.createElement('img');
        blobImage.className="preview"; //← Class name is given to img generated by createElement
      blobImage.setAttribute('src', blob);
      //Display the generated HTML element in the browser
    document.getElementById('idea-image').addEventListener('change', function(e){
      //Delete an existing image only if the image is displayed
      const imageContent = document.querySelector('img');
      if (imageContent){
      const file = e.target.files[0];
      const blob = window.URL.createObjectURL(file);

** Finally, specify the size of the image with CSS. ** **


.preview {
  height: 250px;
  width: 250px;
  object-fit: contain;

Implementation completed

Thanks to the images being displayed, it is easier to understand the image you have selected.


It was a good review because I didn't implement it using javascript very much. Also, I learned how to give a class name to the element created by createElement, which was a great learning experience.

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