File Upload in Koa.js

Koa.js is a lightweight web framework for node.js that provides a simple and flexible way to build web applications. One of the core features of Koa.js is its support for file uploads, which makes it easy to handle files from forms or other data sources. In this article, we will explore how to use the koa-bodyparser middleware to parse incoming requests with file attachments and store them on the server.

First, we need to install the necessary packages:

npm install koa body-parser express --save

This command will install Koa, body-parser, Express, and any dependencies required by these packages. Body-parser is a middleware that parses incoming requests with JSON, raw, text, and URLencoded formats. We'll be using it to parse the request headers for files uploaded to our server.

Next, let's create a new Koa app:

const Koa = require('koa');
const bodyParser = require('body-parser');

const app = new Koa();
app.use(bodyParser.json());
app.use(bodyParser.urlencoded({ extended: false }));

app.listen(3000);

Here, we're creating a new instance of the Koa class and using the body-parser middleware to parse incoming requests with JSON or URL-encoded formats. We also listen on port 3000 for incoming requests.

Now let's create a route handler that responds to file uploads:

app.post('/upload', async (ctx, next) => {
  const file = ctx.request.files.file;

  if (!file) {
    ctx.body = 'No file uploaded';
    return;
  }

  ctx.body = `Received file: ${file.name}, type: ${file.type}`;
});

In this route handler, we're using the req object provided by Koa to access the request headers for the file upload. We retrieve the file object from the files property of the req object and check if it exists. If the file is missing or invalid, we return an error message. Otherwise, we display a success message that includes the filename and mime type.

To test this route handler, we can create a simple HTML form that sends a file to our server:

<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <title>File Upload</title>
  </head>
  <body>
    <form method="post" enctype="multipart/form-data" action="/upload">
      <input type="file" name="file" />
      <button type="submit">Upload File</button>
    </form>
  </body>
</html>

This form uses the POST method and specifies the enctype attribute as "multipart/form-data", which tells the browser to send the file attachment as part of the request. We also set the action attribute to "/upload" to specify the route handler that will handle the file upload.

We can run our Koa app with the following command:

node server.js

And then open our HTML form in a web browser and select a file to upload. Once we submit the form, our Koa app should receive the file and respond with a message indicating its name and type.

In conclusion, this article has demonstrated how to use the koa-bodyparser middleware to parse incoming requests with file attachments and store them on the server using Koa.js. We have shown how to create a simple route handler that responds to file uploads and tested it with an HTML form.

File Upload in Koa.js

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