Simple Javascript Expense List (Progressive Web App)

Welcome to a tutorial on how to create a simple expense list with pure Javascript. Yep, there are a ton of such “expense list” examples on the Internet. So here’s one that is slightly different – An offline-capable expense list web app. Read on!

 

 

TABLE OF CONTENTS

 

 

EXPENSE LIST DEMO

 

 

PART 1) THE HTML

<!-- (A) ADD NEW RECORD -->
<form id="add_form" onsubmit="return track.add()">
  <input id="add_date" type="date" required>
  <input id="add_name" type="text" placeholder="Item Name" required>
  <input id="add_amt" type="number" min="1" step="0.01" placeholder="Amount" value="1.00" required>
  <input type="submit" value="Add">
</form>
 
<!-- (B) RECORDS -->
<div id="rec_wrap"></div>

The HTML layout is very straightforward:

1. A <form> to “add a new expense entry” – Date, item name, and amount.
2. An empty <div> to show the expense entries.

 

PART 2) THE JAVASCRIPT

2A) PROPERTIES

var track = {
  // (A) PROPERTIES
  data : {},    // expenses data
  hDate : null, // html add item date
  hName : null, // html add item name
  hAmt : null,  // html add item amount
  hWrap : null, // html records wrapper
};

The var track object will contain all the mechanics that drive the app. At the very top of the script, we begin by defining the properties.

• track.data An object to hold the expense entries. Will go through more below in 2E.
• track.hSOMETHING Reference to the HTML elements.

 

 

2B) SAVE EXPENSE ENTRIES

// (B) SUPPORT FUNCTION - SAVE TO LOCAL STORAGE
save : () => localStorage.setItem("expenses", JSON.stringify(track.data)),

Next, we have track.save() that saves track.data into the localStorage. For those who are new, track.data will disappear once the user navigates away from the page. This is why we have to save it into the persistent localStorage whenever changes are made.

 

2C) INITIALIZE

// (C) INIT
init : () => {
  // (C1) GET HTML ELEMENTS
  track.hDate = document.getElementById("add_date");
  track.hName = document.getElementById("add_name");
  track.hAmt = document.getElementById("add_amt");
  track.hWrap = document.getElementById("rec_wrap");
 
  // (C2) DEFAULT TODAY'S DATE
  track.hDate.valueAsDate = new Date();
 
  // (C3) LOAD RECORDS FROM LOCAL STORAGE
  let data = localStorage.getItem("expenses");
  if (data != null) { track.data = JSON.parse(data); }
 
  // (C4) DRAW RECORDS
  track.draw();
},
window.addEventListener("DOMContentLoaded", track.init);

track.init() will run on page load, and it does what its name implies – Initiate the app.

• (C1) Get the related HTML elements.
• (C2) Set the default date in the “add entry” HTML form to today.
• (C3) Restore the entries from localStorage.
• (C4) Draw the expense records.

 

2D) DRAW EXPENSE ENTRIES

// (D) DRAW RECORDS
draw : () => {
  // (D1) EMPTY WRAPPER
  track.hWrap.innerHTML = "";
 
  // (D2) LOOP & DRAW RECORDS
  let row, total = 0;
  for (let date in track.data) { for (let i in track.data[date]) {
    let entry = track.data[date][i];
    total += parseFloat(entry[1]);
 
    row = document.createElement("div");
    row.className = "row";
    row.innerHTML = `
    <input type="button" value="X" onclick="track.del('${date}', ${i})">
    <div class="name">[${date}] ${entry[0]}</div>
    <div class="amt">$${entry[1]}</div>`;
    track.hWrap.appendChild(row);
  }}
 
  // (D3) TOTAL
  row = document.createElement("div");
  row.className = "row total";
  row.innerHTML = `<div class="name">Total Expenses</div><div class="amt">$${total.toFixed(2)}</div>`
  track.hWrap.appendChild(row);
},

Right, this seems confusing at first, but keep calm and look closely. We are just looping through track.data, creating the HTML, and inserting them into <div id="rec_wrap">.

 

 

2E) ADD EXPENSE ENTRY

// (E) ADD ENTRY
add : () => {
  // (E1) PUSH NEW ENTRY
  if (track.data[track.hDate.value]==undefined) { track.data[track.hDate.value] = []; }
  track.data[track.hDate.value].push([track.hName.value, track.hAmt.value]);
 
  // (E2) SORT & SAVE TO LOCALSTORAGE
  // CREDITS : https://www.w3docs.com/snippets/javascript/how-to-sort-javascript-object-by-key.html
  track.data = Object.keys(track.data).sort().reduce((r,k) => (r[k] = track.data[k], r), {});
  track.save();
 
  // (E3) RESET FORM
  track.hName.value = "";
  track.hAmt.value = "1.00";
 
  // (E4) DRAW RECORDS
  track.draw();
  return false;
},

As you already know track.data holds the expense entries. Here’s the data structure:

track.data = {
  "YYYY-MM-DD" : [["NAME", "AMOUNT"], ["NAME", "AMOUNT"], ...],
  "YYYY-MM-DD" : [["NAME", "AMOUNT"], ["NAME", "AMOUNT"], ...],
  ...
};

That’s right, track.data is an object organized by DATE : ARRAY OF ITEMS. In track.add(), we are simply pushing more entries into this object, sorting it, then updating it into localStorage.

 

2F) REMOVE EXPENSE ENTRY

// (F) REMOVE ENTRY
del : (date, i) => { if (confirm("Delete Entry?")) {
  track.data[date].splice(i, 1);
  if (track.data[date].length==0) { delete track.data[date]; }
  track.save();
  track.draw();
}}

How do we remove an entry from track.data? We simply splice the selected entry out, and update localStorage.

 

PART 3) PROGRESSIVE WEB APP

3A) HTML META

<head>
  <!-- ANDROID + CHROME + APPLE + WINDOWS APP -->
  <link rel="icon" href="favicon.png" type="image/png">
  <meta name="mobile-web-app-capable" content="yes">
  <meta name="theme-color" content="white">
  <link rel="apple-touch-icon" href="icon-512.png">
  <meta name="apple-mobile-web-app-capable" content="yes">
  <meta name="apple-mobile-web-app-status-bar-style" content="black">
  <meta name="apple-mobile-web-app-title" content="JS Expense">
  <meta name="msapplication-TileImage" content="icon-512.png">
  <meta name="msapplication-TileColor" content="#ffffff">
 
  <!-- WEB APP MANIFEST -->
  <!-- https://web.dev/add-manifest/ -->
  <link rel="manifest" href="3a-manifest.json">
 
  <!-- SERVICE WORKER -->
  <script>
  if ("serviceWorker" in navigator) { navigator.serviceWorker.register("3b-worker.js"); }
  </script>
</head>

At this stage, we already have a fully functioning expense tracker; This step is completely optional. But to bring it one level up to an “installable progressive web app”, we only need a few more things.

• Specifying the icons is kind of optional. It’s a pain in the “S” as different platforms/browsers use different icon sizes. I usually just define a huge 512X512 icon, and let the platforms resize it.
• Define a web app manifest.
• Install a service worker.

 

 

3B) WEB MANIFEST

{
  "short_name": "Expenses",
  "name": "JS Expenses",
  "icons": [{
    "src": "favicon.png",
    "sizes": "64x64",
    "type": "image/png"
  }, {
    "src": "icon-512.png",
    "sizes": "512x512",
    "type": "image/png"
  }],
  "start_url": "1-track-expense.html",
  "scope": "/",
  "background_color": "white",
  "theme_color": "white",
  "display": "standalone"
}

The manifest file should be pretty self-explanatory – It contains data on your app name, icons, and general settings.

 

3C) SERVICE WORKER

// (A) CREATE/INSTALL CACHE
self.addEventListener("install", evt => {
  self.skipWaiting();
  evt.waitUntil(
    caches.open("JSExpenses")
    .then(cache => cache.addAll([
      "favicon.png",
      "icon-512.png",
      "1-track-expense.html",
      "2-track-expense.css",
      "2-track-expense.js",
      "3a-manifest.json"
    ]))
    .catch(err => console.error(err))
  );
});
 
// (B) CLAIM CONTROL INSTANTLY
self.addEventListener("activate", evt => self.clients.claim());
 
// (C) LOAD FROM CACHE FIRST, FALLBACK TO NETWORK IF NOT FOUND
self.addEventListener("fetch", evt => evt.respondWith(
  caches.match(evt.request).then(res => res || fetch(evt.request))
));

For those who are new once again, a “service-worker” is simply Javascript that runs in the background.

• (A & B) In this one, we save the entire project into the browser cache.
• (C) “Hijack” the fetch requests. Load from the cache if the requested file is found, fallback to load from the network if not.

In other words, this worker will help to support “offline mode” – Run from the browser cache.

 

 

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EXAMPLE CODE DOWNLOAD

Click here for the source code on GitHub gist, just click on “download zip” or do a git clone. I have released it under the MIT license, so feel free to build on top of it or use it in your own project.

 

 

NOTES ON PERFORMANCE

A quick note here that localStorage is not a database, it can only save flat strings. In this example, we are saving data by converting an object into a string with JSON.stringify(). To restore the data, we convert a string back to an object with JSON.parse().

This is by all means, not great for performance. If you want a “real Javascript database”, check out indexed databases. Links below.

 

 

COMPATIBILITY CHECKS

• Arrow Functions – CanIUse
• Local Storage – CanIUse
• Service Worker – CanIUse
• Add To Home Screen – CanIUse

This example will work on most browsers. But offline support and “install to home screen” will only work on modern “Grade A” browsers.

 

LINKS & REFERENCES

• Indexed DB API – MDN
• Example on Codepen – Simple Javascript Expense Tracker