How to use Express with Deno

Express is a popular web framework known for being simple and unopinionated with a large ecosystem of middleware.

This How To guide will show you how to create a simple API using Express and Deno.

View source here.

Create main.ts

Let’s create main.ts:

touch main.ts

In main.ts, let’s create a simple server:

// @deno-types="npm:@types/express@4.17.15"
import express from "npm:express@4.18.2";

const app = express();

app.get("/", (req, res) => {
  res.send("Welcome to the Dinosaur API!");
});

app.listen(8000);

Let’s run this server:

deno run -A main.ts

And point our browser to localhost:8000. You should see:

Welcome to the Dinosaur API!

Add data and routes

The next step here is to add some data. We’ll use this Dinosaur data that we found from this article. Feel free to copy it from here.

Let’s create data.json:

touch data.json

And paste in the dinosaur data.

Next, let’s import that data into main.ts. Let’s add this line at the top of the file:

import data from "./data.json" assert { type: "json" };

Then, we can create the routes to access that data. To keep it simple, let’s just define GET handlers for /api/ and /api/:dinosaur. Add the below after the const app = express(); line:

app.get("/", (req, res) => {
  res.send("Welcome to the Dinosaur API!");
});

app.get("/api", (req, res) => {
  res.send(data);
});

app.get("/api/:dinosaur", (req, res) => {
  if (req?.params?.dinosaur) {
    const found = data.find(item => item.name.toLowerCase() === req.params.dinosaur.toLowerCase());
    if (found) {
      res.send(found)
    } else {
      res.send("No dinosaurs found.");
    }
  }
});

app.listen(8000);

Let’s run the server with deno run -A main.ts and check out localhost:8000/api. You should see a list of dinosaurs:

[
  {
    "name": "Aardonyx",
    "description": "An early stage in the evolution of sauropods."
  },
  {
    "name": "Abelisaurus",
    "description": "\"Abel's lizard\" has been reconstructed from a single skull."
  },
  {
    "name": "Abrictosaurus",
    "description": "An early relative of Heterodontosaurus."
  },
...

And when we go to localhost:8000/api/aardonyx:

{
  "name": "Aardonyx",
  "description": "An early stage in the evolution of sauropods."
}

Great!