how to create web scrapper with react framework and nextjs

NextJS is a NodeJS framework that allows us to write server-side rendering React web application.
So there are two keywords here: server-side rendering and React.

• As we may have known, React is a JavaScript UI library that allows us to build user interface. React use virtual dom and build with components so that we can re-use them in multiple places. There are ton of articals or tutorials about React, here is it’s official web site: https://reactjs.org/
  
• How about server-side rendering? Normally, React libarary uses client-side rendering, which means that when we access the web page, all required JavaScript would be downloaded to client then being rendered to DOM elements. This is absolutely best practice, especially for single page application, that we don’t have to load the page again when navigating around. But there is a problem with client-side rendering. It is not very good for SEO. To solve this problem, one of solution is to use server-side rendering. That is, the initial render would be performed by server side, then sent to client. From that point, other rendering would be taken over by client side. By doing this, we can both decrease the first load size, and also increase SEO optimization and still using React library.
  

Why use NextJS?

By using NextJS, we can use both server-side rendering technique and using ReactJS library. An other plus to count is that it works smoothly with ExpressJS which is best NodeJS web framework right now. Last but not least, when using NextJS, I can easily configure default routes by seperating files, something similar to PHP. For example, when access to /sample_route, it would, by default executes content in sample_route.js in server side. This is very convenient if we want to build a quick demo application. Of course, still we can modify this behavior to make routing more structural.
NextJS GitHub page: https://github.com/zeit/next.js/

Implementation

In this note, I would like to introduce how I used NextJS to build a sample web scraper. The original idea is to use website-scraper package from npm. They provides a sample which uses AngularJS, so I want to create my own version using React.
Let’s start the steps.

Preparation

Make sure to latest version of NodeJS/NextJS. In my case:

• Node version: v9.3.0
  
• npm version: 5.6.0
  
• I also use boilerplates, you can search for some of them in this link. I chosen to use next-express-bootstrap-boilerplate which provide NextJS in ExpressJS framework with support of bootstrap and SCSS. You can use both npm or yarn with this boilerplate. Please follow their GitHub manual for installation instruction.
  

First, install npm package

sudo npm i -g next-express-bootstrap-boilerplate

Then cd to source code folder, run command:

next-boilerplate

After everything installed, run web application with command:

npm run dev

or

yarn dev

Here is how the default display look like:

You can check boilerplate GitHub page to understand structure of source code. The basic idea is that when accessing / root route, it would execute file /apps/page/index.js, and for /profile, it would execute file /apps/page/profile.js to render UI. This is quite straightforward and easy to understand for beginner.
Since we don’t need /profile route, I delete file /apps/page/profile.js and modify /apps/page/index.js to add UI for URL input, submit form. Here is how new UI look like:

The application structure is quite simple:

• An input form to input URL to scrape
  
• When submitting, it calls React component Index function doSubmitUrl to do POST call to /scrape_url using fetch. To understand fetch, refer to how to Use Fetch.
  
• In server side, app.js, add a function to handle POST /scrape_url:
  

    app.post('/scrape_url', (req, res) => {
        const scrapeUrl = req.body.url;
        if (!scrapeUrl) {
            return res.status(500).send('Please provide a valid URL');
        }
        const folderName = (new Date()).getTime();
        const options = {
            urls: [scrapeUrl],
            directory: `tmp/${folderName}`,
        }

        scrape(options).then((result) => {
            const zipFile = `./tmp/${folderName}.zip`;
            zipFolder(options.directory, zipFile, (err) => {
                if (err) {
                    console.log(err);
                    return res.status(500).send('zip file failed');
                } else {
                    return res.download(zipFile);
                }
            })
        }).catch((err) => {
            console.log(err);
            return res.status(500).send('zip file failed');
        });
    });

This responds a file to client and in client side, we render a link with blob response data, as a part of doSubmitUrl function:

    doSubmitUrl() {
        const data = { url: this.state.url }
        const url = '/scrape_url';
        fetch(url, {
            method: 'POST',
            body: JSON.stringify(data),
            headers: new Headers({
                'Content-Type': 'application/json'
            }),
        })
        .then((response) => response.blob())
        .then((blob) => {
            const link=document.createElement('a');
            link.href=window.URL.createObjectURL(blob);
            link.text=`${this.state.url}.zip`;
            const downloadLink = document.getElementById('downloadLink');
            downloadLink.appendChild(link);
        })
        .catch(error => console.error('Error:', error));
    }

Here is my whole project in GitHub: website-scraper-demo-nextjs

Conclusion

In this post I introduced how to use NextJS to build a website scraper. NextJS, with a boilerplate helps us to create initial source code quickly so we can begin to code our real applications. I don’t have a chance to try NextJS for larger project but for simple demos, this is effective way to make thing done. And with ExpressJS behide, there should be no problem to use NextJS in larger scale. There are some more websites built with NextJS listed here: https://github.com/zeit/next.js/issues/1458

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