How I Built a Simple Excel Plugin with the Office JavaScript API

Recently, I decided to build something fun and useful: a custom Excel plugin that can pull data from an external API and show it directly in a spreadsheet. If you’ve ever thought about building your own Excel add-in, or you’re just curious how it works, this post is for you!

🎯 What I Wanted to Build
The goal was simple:

Let users click a button inside Excel, fetch data from an API, and insert it into the sheet—automatically.

Think of it like a mini data importer right inside Excel. No copy-pasting, no manual formatting—just one button that does the work.

🧰 The Tools I Used

1. Office JavaScript API (office.js) – to talk to Excel
2. HTML/CSS – to design the UI
3. JavaScript – for logic
4. Fabric UI – for a nice-looking Microsoft-style layout

🛠️ How It Works (The Simple Version)
When the plugin loads:

1. It shows a welcome screen
2. There’s a “Run” button
3. When you click “Run”, it grabs some mock data (like names and emails)
4. It inserts that data into Excel starting from cell A1

Here's a peek at the main code that adds the data to Excel:
await Excel.run(async (context) => {
const sheet = context.workbook.worksheets.getActiveWorksheet();
const range = sheet.getRange("A1").getResizedRange(data.length - 1, data[0].length - 1);
range.values = data;
await context.sync();
});
And the fake API data looks like this:
[
["ID", "Name", "Email"],
[1, "Alice", "[e-mail]"],
[2, "Bob", "[e-mail]"],
[3, "Charlie", "[e-mail]"],
]
Right now it's mocked with setTimeout(), but this could easily be replaced with a real API call.

🤔 Why Even Bother?
Microsoft Excel is used by millions of people. If you can build something that works inside Excel, you’re helping users right where they already work—no extra tools needed.

This type of plugin is useful for:

1. Importing sales data from a company database
2. Pulling CRM contact lists into a spreadsheet
3. Syncing reports from online dashboards into Excel

💡 Final Thoughts
I didn’t expect working with Excel to be this fun. The Office JavaScript API gives you a ton of power to build real tools. If you're looking to get into building add-ins, I highly recommend starting with a simple use case like this.

Have questions or want to try it yourself? I’m happy to help!

---

## 📁 Source Code

Want to dive into the code? It’s open-source!

🔗 Check out the GitHub repo here