Simple Offline Javascript Grocery List PWA (Free Download)

Welcome to a quick tutorial on how to create a simple Javascript grocery list. Ah yes, this is a classic school assignment that has never changed for decades. There are probably a ton of these on the Internet already, so I figured to create one that is “updated” – A grocery list progressive web app that works offline. Read on!

 

 

TABLE OF CONTENTS

 

 

GROCERY LIST DEMO

 

 

PART 1) THE HTML

<div id="gro-wrap">
  <h1>GROCERY LIST</h1>
 
  <!-- (A) ADD ITEM -->
  <form id="gro-form">
    <input type="number" id="gro-qty" min="1" value="1" placeholder="Quantity" required disabled>
    <input type="text" id="gro-item" placeholder="Item Name" required disabled>
    <button id="gro-add" class="material-icons" disabled>add</button>
  </form>
 
  <!-- (B) ITEM LIST -->
  <div id="gro-list"></div>
</div>

The HTML is very straightforward, there are only 2 sections to the user interface.

1. A simple “add item” <form> with 2 fields – Quantity and item name.
2. An empty <div> container to generate the grocery list into.

 

PART 2) GROCERY LIST INITIATE

var glist = {
  // (A) INITIALIZE GROCERY LIST
  items : [], // current grocery list
  hqty : null, // html add quantity field
  hitem : null, // html add item field
  hlist : null, // html <div> grocery list
  init : () => {
    // (A1) GET HTML ELEMENTS
    glist.hqty = document.getElementById("gro-qty");
    glist.hitem = document.getElementById("gro-item");
    glist.hlist = document.getElementById("gro-list");
 
    // (A2) ENABLE FORM
    glist.hqty.disabled = false;
    glist.hitem.disabled = false;
    document.getElementById("gro-add").disabled = false;
    document.getElementById("gro-form").onsubmit = glist.add;
 
    // (A3) RESTORE PREVIOUS GROCERY LIST
    if (localStorage.items == undefined) { localStorage.items = "[]"; }
    glist.items = JSON.parse(localStorage.items);
 
    // (A4) DRAW HTML GROCERY LIST
    glist.draw();
};
window.addEventListener("load", glist.init);

How does grocery list Javascript work? Let us start with glist.init(), this function will run on page load.

• (A1) Get all the related HTML elements.
• (A2) Enable the “add item” HTML form.
• (A3) Now, this is where the magic happens.
  • glist.items is an array that stores the actual grocery list.
  • But as you know, variables will disappear once the user navigates away. So we will use localStorage.items to store the grocery list in a more permanent manner.
  • This section simply initializes an empty array if it is a first-time user, or restores the grocery list from a previous session.
• (A4) Draw the HTML grocery list when the init is done.

 

 

PART 3) ADD A NEW ITEM

// (B) SAVE GROCERY LIST INTO LOCAL STORAGE
save : () => {
  if (localStorage.items == undefined) { localStorage.items = "[]"; }
  localStorage.items = JSON.stringify(glist.items);
},
 
// (C) ADD NEW ITEM TO THE LIST
add : evt => {
  // (C1) ADD NEW ITEM TO LIST
  glist.items.push({
    qty : glist.hqty.value, // item quantity
    name : glist.hitem.value, // item name
    got : false // item accquired
  });
  glist.save();
 
  // (C2) RESET HTML ADD FORM
  glist.hqty.value = 1;
  glist.hitem.value = "";
 
  // (C3) REDRAW HTML GROCERY LIST
  glist.draw();
  return false;
},

This can be a little intimidating to beginners, but keep calm and look closely.

• (C) glist.add() is fired when the user adds a new item.
• (C1) We create a new object { qty: QUANTITY, name: ITEM NAME, got: STATUS }, and push it into the glist.items array.
• (B) Save the updated grocery list into localStorage.items.

Yep, that’s about it.

 

PART 4) DELETE ITEM & TOGGLE STATUS

// (D) DELETE SELECTED ITEM
delete : id => { if (confirm("Remove this item?")) {
  glist.items.splice(id, 1);
  glist.save();
  glist.draw();
}},
 
// (E) TOGGLE ITEM BETWEEN "ACCQUIRED" & "NOT YET"
toggle : id => {
  glist.items[id].got = !glist.items[id].got;
  glist.save();
  glist.draw();
},

• (D) To delete an item, we simply remove it from the glist.items array, then update localstorage.items.
• (E) To update the “got it/not yet” status, we simply update the respective glist.items[id].got flag, then update localstorage.items.

 

 

PART 5) DRAW HTML GROCERY LIST

// (F) DRAW THE HTML GROCERY LIST
draw : () => {
  // (F1) RESET HTML LIST
  glist.hlist.innerHTML = "";
 
  // (F2) NO ITEMS
  if (glist.items.length == 0) {
    glist.hlist.innerHTML = "<div class='item-row item-name'>No items found.</div>";
  }
 
  // (F3) DRAW ITEMS
  else { for (let i in glist.items) {
    // (F3-1) ITEM ROW
    let row = document.createElement("div");
    row.className = glist.items[i].got ? "item-row yes" : "item-row no";
    glist.hlist.appendChild(row);
 
    // (F3-2) DELETE BUTTON
    let del = document.createElement("button");
    del.className = "item-del material-icons";
    del.innerHTML = "delete";
    del.onclick = () => glist.delete(i);
    row.appendChild(del);
 
    // (F3-3) ITEM QUANTITY & NAME
    let name = document.createElement("div");
    name.innerHTML = `${glist.items[i].qty} X ${glist.items[i].name}`;
    name.className = "item-name";
    row.appendChild(name);
 
    // (F3-4) ITEM ACCQUIRED
    let ok = document.createElement("button");
    ok.className = "item-ok material-icons";
    ok.innerHTML = glist.items[i].got ? "done" : "clear";
    ok.onclick = () => glist.toggle(i);
    row.appendChild(ok);
  }}
}

This function simply loops through the glist.items array to generate the HTML grocery list.

 

PART 6) PROGRESSIVE WEB APP

At this stage, we already have a fully functioning grocery list. But we can further enhance it into an offline-capable and installable progress web app. No need to panic, it actually only requires a couple more things – A web manifest and a service worker in particular.

 

 

6A) HTML META

<!-- ANDROID + CHROME + APPLE + WINDOWS APP -->
<meta name="viewport" content="width=device-width, initial-scale=1.0, maximum-scale=1.5">
<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 Grocery List">
<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="grocery-manifest.json">
 
<!-- SERVICE WORKER -->
<script>
if ("serviceWorker" in navigator) {
  navigator.serviceWorker.register("grocery-worker.js");
}
</script>

In the <head> section of the HTML, we will add metadata for:

• App icons. It is kind of painful here as everyone uses a different icon size. I just do it the lazy way, create a huge 512 X 512 icon and let whatever Apple/Android/Windows do their own resizing.
• Define the web app manifest.
• Register a service worker.

 

6B) WEB APP MANIFEST

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

What the heck is a “web app manifest”? This should be self-explanatory. It contains information about your web app – The name, icon, description, theme color, etc…

 

6C) SERVICE WORKER

// (A) CREATE/INSTALL CACHE
self.addEventListener("install", evt => {
  self.skipWaiting();
  evt.waitUntil(
    caches.open("JSGrocery")
    .then(cache => cache.addAll([
      "favicon.png",
      "icon-512.png",
      "grocery-list.html",
      "grocery-list.css",
      "grocery-list.js",
      "grocery-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))
});

Finally, a “service worker” is simply a piece of Javascript that runs in the background. In this one:

• (A) We will cache the HTML/CSS/JS/images into the browser.
• (C) “Hijack” the fetch requests, load from the cache if the requested file is saved in the cache.

In other words, offline support. Even if the user is not connected to the Internet, the web app will still load from the 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.

 

 

COMPATIBILITY CHECKS

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

This example will work on most browsers, but the PWA offline features will only work on the “Grade A” ones.

 

LINKS & REFERENCES

• Progressive Web App – Google Developers
• Example On CodePen – JS Grocery List