Omikuji Fortune Telling App

Omikuji is a Japanese word means random fortunes. In Monaca, app development is done using HTML and JavaScript just like webpages. JavaScript is a scripting language with simple syntax and functions, and often used for smartphone development compared to other languages.

Tested Environment

  • Android 7.0
  • iOS 10.1.1

File Components

File Description
index.html The startup page
images/*.png Image files used in this application

HTML Explanation

The contents of the HTML body section are shown below:

<div id="hako">
    <img id="saisyo" src="images/omikuji-box.png" />
    <img id="kekka" style="display : none;"/>
<div id="bottombar">
    <img id="button" src="images/omikuji-btn-hajimeru.png" onclick="omikuji()">

There are two div tags spanning lines 1 through 4 and lines 5 through 7, with their IDs set to hako and bottombar , respectively. These IDs are referenced in the style sheet, which is discussed below.

The div tag is used for grouping other tags. For example, the div tag with the ID hako contains img tags with the IDs saisyo and kekka . img tag is used to display an image. These two tags display images for the omikuji box (displayed immediately after startup) and omikuji result, respectively.

In order to display the image of the omikuji box when the app starts, the image is specified using the src attribute of the img tag with the ID saisyo. In contrast, the kekka img tag has no src attribute. Instead, a style="display: none" attribute has been provided. This is an example of how to include a style sheet definition (discussed below) in HTML, and this means that the image will not be displayed onscreen when the file is loaded. The fortune telling result image is set and displayed using the JavaScript program discussed below.

Similarly, the div tag with the ID bottombar also contains an img tag. In addition to the src attribute, an onclick attribute has also been provided. The onclick attribute contains JavaScript code to be called when the image is clicked or tapped. In this example, when the fortune telling start button is tapped, the JavaScript omikuji() function is called. The omikuji() function prepares the fortune telling results and displays them onscreen.

Style Sheet Explanation

The style sheet is included in the HTML head tag using the style tag. The style sheet code itself is shown below. There are three main groups of definitions: definitions for the body tag, definitions for the tag with the ID hako , and definitions for the tag with the ID bottombar.

body {
    background: url("images/omikuji-bg.png") 100% 100%;
    margin: 0;
    padding: 0;
    text-align: center;
#hako {
    position: absolute;
    width: 100%;
    top: 10%;
#bottombar {
    position: absolute;
    bottom: 30px;
    width: 100%;

The four properties (background , margin , padding , and text-align) are applied to set the styling for the body tag. The background property is used to set the background image. In this example, the image images/omikuji-bg.png will be enlarged to fill the body tag, i.e., the entire page. The margin and padding properties are used to specify the page margins. Since they are both set to 0 in this example, there are no margins. The text-align property is used to set text alignment. In this example, text is center aligned.

As mentioned in the HTML explanation, #hako identifies the div tag used to display the omikuji box and result images, and #bottombar identifies the div tag used to display the start button. These style sheet definitions make use of the position , bottom , top , and width properties. When the position property is set to absolute , positioning is done using absolute coordinates. In this example, both divs will use coordinates relative to their parent tag, the body tag. The bottom and top properties set the position from the bottom or top.

This app refers to the external style sheet components/loader.css. It contains style sheet definitions used by libraries loaded by Monaca plugins. However, it has no significance here since this sample app does not make use of Monaca plugins included in the style sheets.

JavaScript Explanation

The JavaScript code is shown below:

function omikuji (){
  var dice = Math.floor(Math.random() * 3);
  var image_name;
  if (dice == 0) {
      image_name = "omikuji-daikichi.png";
  } else if  (dice == 1) {
      image_name = "omikuji-chuukichi.png";
  } else {
      image_name = "omikuji-hei.png";

  document.getElementById("saisyo").style["display"] = "none";
  document.getElementById("kekka").src = "images/" + image_name;
  document.getElementById("kekka").style["display"] = "inline";
  document.getElementById("button").src = "images/omikuji-btn-yarinaosu.png";

Lines 1 through 16 contain the definition of the omikuji function. When the start button is tapped, this function will be executed. On line 2, the Math.floor and Math.random functions are combined to generate a random number from 0 to 3, which is assigned to the dice variable. On lines 4 through 11, the variable image_name is assigned an image file name according to the value of the dice variable.

On lines 12 through 15, the document.getElementById function is used to modify the style sheet and replace images. This is referred to as DOM (Document Object Model) manipulation, and is used to dynamically update. In the following example, the src attribute of the element (HTML tag) with the ID kekka is modified.

document.getElementById("kekka").src = "images/" + image_name;

Since, as described above, the image_name variable is set to the name of the image file corresponding to the omikuji result, this technique can be used to display the image for the fortune telling result onscreen.