Category: JavaScript Answers

To serve static files with Express.js, we can use the express.static middleware.

For instance, we can write:

const express = require('express')
const app = express()
const port = 3000
app.use(express.static(__dirname + '/public'));

app.get('/', (req, res) => {
  res.send('hello world')
})

app.listen(port, () => {
  console.log(`Example app listening at http://localhost:${port}`)
})

We call app.use with express.static(__dirname + ‘/public’) to serve the public folder in the project folder as the static folder.

This will expose the folder’s contents to the public.

Therefore, if we have a foo.txt file in the public folder, we can go to /foo.txt to see its contents.

To to fix the Express.js ‘req.body undefined’ error, we can use the body-parser middleware to parse the POST form fields into a JavaScript object.

To install the package, we run:

npm install --save body-parser

Then we can write:

const express = require('express')
const app = express()
const port = 3000
const bodyParser = require('body-parser')
app.use(bodyParser.json());
app.use(bodyParser.urlencoded({
  extended: true
}));

app.post('/', (req, res) => {
  res.json(req.body)
})

app.listen(port, () => {
  console.log(`Example app listening to ${port}`)
})

to add body-parser into our app with:

app.use(bodyParser.json());
app.use(bodyParser.urlencoded({
  extended: true
}));

Now we can parse JSON or URL encoded request data into the req.body property.

Therefore, when we send request data into the POST / route, we see the request value returned as the response in an object.

To return JSON responses with Express, we can use the res.json method to return a JSON response.

For instance, we can write:

const express = require('express')
const app = express()
const port = 3000
app.set('json spaces', 2);

app.get('/', (req, res) => {
  const obj = { foo: 1, bar: 2, baz: 3 }
  res.json(obj)
})

app.listen(port, () => {
  console.log(`Example app listening at http://localhost:${port}`)
})

We call app.set to set the 'json spaces' setting to 2 to make the indentation of the JSON 2 spaces.

Then in the GET / route, we call res.json with an object to return the obj object as the response.

Therefore, the response we get is:

{
  "foo": 1,
  "bar": 2,
  "baz": 3
}

when we go to the GET / route.

To fix the ‘Error: request entity too large’ in Express, we can set the limit option when we add body-parser into our Express app.

For instance, we can write:

const express = require('express')
const app = express()
const port = 3000
const bodyParser = require('body-parser')
app.use(bodyParser.json({ limit: '50mb' }));
app.use(bodyParser.urlencoded({ limit: '50mb', extended: true }));

app.post('/', (req, res) => {
  res.json(req.body)
})

app.listen(port, () => {
  console.log(`Example app listening at http://localhost:${port}`)
})

to set the max size of JSON and URL encoded request data to 50MB by setting limit to '50mb' .

To access POST form fields values with Express, we can use the body-parser middleware to parse the POST form fields into a JavaScript object.

To install the package, we run:

npm install --save body-parser

Then we can write:

const express = require('express')
const app = express()
const port = 3000
const bodyParser = require('body-parser')
app.use(bodyParser.json());
app.use(bodyParser.urlencoded({
  extended: true
}));

app.post('/', (req, res) => {
  res.json(req.body)
})

app.listen(port, () => {
  console.log(`Example app listening at http://localhost:${port}`)
})

to add body-parser into our app with:

app.use(bodyParser.json());
app.use(bodyParser.urlencoded({
  extended: true
}));

Now we can parse JSON or URL encoded request data into the req.body property.

Therefore, when we send request data into the POST / route, we see the request value returned as the response in an object.