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:

import
 
express
 
from
 
"npm:[email protected]"
;

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!