Category: JavaScript Answers

Sometimes, we want to parse a HTML page with Node.js.

In this article, we’ll look at how to parse a HTML page with Node.js.

How to parse a HTML page with Node.js?

To parse a HTML page with Node.js, we can use the Cheerio library.

To install it, we run

npm i cheerio

Then we write

const cheerio = require('cheerio');
const $ = cheerio.load('<h2 class="title">Hello world</h2>');

$('h2.title').text('Hello there!');
$('h2').addClass('welcome');

$.html();

to call cheerio.load to load the HTML string into the $ object.

Then we call $ with the CSS selector string to select the elements we want to manipulate.

And we call text to set the text of the h2 element with class title.

And we call addClass to add the welcome class to all h2 elements.

We return the HTML of the manipulated document with $.html.

To get the HTML string from a web page, we can make a request with any HTTP client.

Conclusion

To parse a HTML page with Node.js, we can use the Cheerio library.

Sometimes, we want to wait N seconds before continuing to the next line with Puppeteer.

In this article, we’ll look at how to wait N seconds before continuing to the next line with Puppeteer.

How to wait N seconds before continuing to the next line with Puppeteer?

To wait N seconds before continuing to the next line with Puppeteer, we can use the waitForTimeout method.

For instance, we write

await page.waitForTimeout(1000);
await frame.waitForTimeout(1000);

to call waitForTimeout to pause script execution on the page or frame for 1 second.

Conclusion

To wait N seconds before continuing to the next line with Puppeteer, we can use the waitForTimeout method.

Sometimes, we want to convert string to buffer with Node.js.

In this article, we’ll look at how to convert string to buffer with Node.js.

How to convert string to buffer with Node.js?

To convert string to buffer with Node.js, we can use the Buffer.from method.

For instance, we write

const buf = Buffer.from(bufStr, 'utf8');

to call Buffer.from with the bufStr string and the encoding of the string to return a buffer created from the string.

Conclusion

To convert string to buffer with Node.js, we can use the Buffer.from method.

Sometimes, we want to get the domain originating the request in Express.js.

In this article, we’ll look at how to get the domain originating the request in Express.js.

How to get the domain originating the request in Express.js?

To get the domain originating the request in Express.js, we can use req.get with the 'host' or 'origin' header string.

For instance, we write

const host = req.get('host');

to call req.get with 'host' to get the hostname of the client that made the request.

For getting the host of cross domain requests, we write

const origin = req.get('origin');

to get the hostname of a cross origin request by calling req.get with 'origin'.

Conclusion

To get the domain originating the request in Express.js, we can use req.get with the 'host' or 'origin' header string.

Sometimes, we want to add gzip compression with Node.js.

In this article, we’ll look at how to add gzip compression with Node.js.

How to add gzip compression with Node.js?

To add gzip compression with Node.js, we can use the built in zlib module.

For instance, we write

const zlib = require('zlib');
const http = require('http');
const fs = require('fs');
http.createServer((request, response) => {
  const raw = fs.createReadStream('index.html');
  let acceptEncoding = request.headers['accept-encoding'];
  if (!acceptEncoding) {
    acceptEncoding = '';
  }

  if (acceptEncoding.match(/\bdeflate\b/)) {
    response.writeHead(200, {
      'content-encoding': 'deflate'
    });
    raw.pipe(zlib.createDeflate()).pipe(response);
  } else if (acceptEncoding.match(/\bgzip\b/)) {
    response.writeHead(200, {
      'content-encoding': 'gzip'
    });
    raw.pipe(zlib.createGzip()).pipe(response);
  } else {
    response.writeHead(200, {});
    raw.pipe(response);
  }
}).listen(3000);

to call createServer with a callback to create a web server.

In the callback, we call zlib.createDeflate and pipe with response to pipe the response for compress .

And we call response.writeHead with an object to set the content-encoding response header to 'gzip‘.

Then we use raw.pipe(zlib.createGzip()).pipe(response) to compress the response with gzip compression.

Conclusion

To add gzip compression with Node.js, we can use the built in zlib module.