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Our headless browser just created a file named screenshot. Great, we have a working Chrome web scraper! First, we launch a new headless browser instance, then we open a new page tab and navigate to the URL provided in the command-line argument.

We also need to make sure to close the headless browser after we are done with our automation. Create a new file named ycombinator-scraper. This method lets us run custom JavaScript code as if we were executing it in the DevTools console. Anything returned from that function gets resolved by the promise.

This method is very handy when it comes to scraping information or performing custom actions. We only had 30 items returned, while there are many more available—they are just on other pages.

There is one more new variable named currentPage which represents the number of the page of results are we looking at currently. We also wrapped our evaluate function in a while loop, so that it keeps running as long as currentPage is less than or equal to pagesToScrape. We added the block for moving to a new page and waiting for the page to load before restarting the while loop. We also used the waitForSelector method to make sure our logic is paused until the page contents are loaded.

Both of those are high-level Puppeteer API methods ready to use out-of-the-box. Hacker News has a relatively simple structure and it was fairly easy to wait for its page load completion. For more complex use cases, Puppeteer offers a wide range of built-in functionality, which you can explore in the API documentation on GitHub.

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Optimizing Our Puppeteer Script The general idea is to not let the headless browser do any extra work. As with other tools, optimization of Puppeteer depends on the exact use case, so keep in mind that some of these ideas might not be suitable for your project. For instance, if we had avoided loading images in our first example, our screenshot might not have looked how we wanted. Anyway, these optimizations can be accomplished either by caching the assets on the first request, or canceling the HTTP requests outright as they are initiated by the website.

You should be aware that when you launch a new headless browser instance, Puppeteer creates a temporary directory for its profile. It is removed when the browser is closed and is not available for use when you fire up a new instance—thus all the images, CSS, cookies, and other objects stored will not be accessible anymore. We can force Puppeteer to use a custom path for storing data like cookies and cache, which will be reused every time we run it again—until they expire or are manually deleted.

However, those assets will still be used when rendering the page. Luckily, Puppeteer is pretty cool to work with, in this case, because it comes with support for custom hooks. The interceptor can be defined in the following way: await page. We can write custom logic to allow or abort specific requests based on their resourceType.

We also have access to lots of other data like request. In the above example, we only allow requests with the resource type of "document" to get through our filter, meaning that we will block all images, CSS, and everything else besides the original HTML response.

Jump Start Node.js

That said, the most basic way to slow down a Puppeteer script is to add a sleep command to it: js await page. You can put this anywhere before browser. Just like limiting your use of third-party services, there are lots of other more robust ways to control your usage of Puppeteer.

One example would be building a queue system with a limited number of workers. This is a fairly common practice when dealing with third-party API rate limits and can be applied to Puppeteer web data scraping as well. However, it has much wider use cases, including headless browser testing, PDF generation, and performance monitoring, among many others. The customer does what they please convert to some spreadsheet format with it.

This is crucial.

Things always break in the wild. Bugs need to be fixed. So in the grand scheme of things, it looks something like this: The initial concept of our program. Introducing Dependencies Now as a disclaimer, I should add that there is a whole world of thought around introducing dependencies into your code. In the meantime let me just say that one of the fundamental conflicts at play is the one between our desire to get our work done quickly i.

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Applying this to our project, I opted to offload the bulk of our PDF processing to the pdfreader module. Here are a few reasons why: It was published recently, which is a good sign that the repo is up-to-date.

This alone is a great sign. Moreover, the dependency, a module called pdf2json, has hundreds of stars, 22 contributors, and plenty of eyeballs keeping a close eye on it. When auditing via NPM 6. So all in all, it seems like a safe dependency to include. They return the same output and only differ in the input: PdfReader.

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The methods ask for a callback, which gets called each time the PdfReader finds what it denotes as a PDF item. There are three kinds.

First, the file metadata, which is always the first item. Second is page metadata.

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It acts as a carriage return for the coordinates of text items to be processed. That script writes that randomized data to JSON files.

How do we do this? Each property in the page object has a y-value for its key, and an array of the text items found at that y-value for its value. The food grade, for this very limited project, technically is safe. So because we want data integrity when reading the PDFs, we just leave everything as a String.

Here we just want something that parses PDFs consistently and accurately. We can use a variety of array and object manipulation functions, and here MDN is your friend. This is the step where everyone has their own preferences.

Some prefer the method that just gets the job done and minimizes dev time. Others prefer to scout for the best algorithm for the job e. Effectively providing a map to follow. All we have to do then is declare a data object to output, iterate over each field we specified, follow the route as per our spec, and assign the value we find at the end to our data object. The diagram above is great for understanding the context of the parsing logic. There are many questions we can ask here and many solutions: is it going to be a command line application?

Is it going to be a consistent server, with a set of API endpoints?We pass the function say as the first parameter to the execute function. Mixed , 76 angelToken: The HackHall Posts page with a liked post. These statements tell Express. With this knowledge, let's get back to our minimalistic HTTP server:.