Chrome extensions offer a versatile way to enhance browsing experiences by adding extra functionality to the Chrome browser. They serve various purposes, like augmenting product pages with additional information on e-commerce sites, scraping data from social media platforms such as LinkedIn or Twitter for analysis or future use, and even facilitating content scraping services for retrieving specific data from websites.
Scraping data from web pages typically involves injecting a content script to parse HTML or traverse the DOM tree using CSS selectors and XPaths. However, modern web applications built with frameworks like React or Vue pose challenges to this traditional scraping method due to their reactive nature.
When visiting a tweet on Twitter, essential details like author information, likes, retweets, and replies aren't readily available in the DOM. However, by inspecting the network tab, one can find API calls containing this hidden data, inaccessible through traditional DOM scraping. It's indeed possible to scrape this information from API calls, bypassing the limitations posed by the DOM.
A secondary method for scraping data involves intercepting API calls by overriding XMLHttpRequest. This entails replacing the native definition of XMLHttpRequest with a modified version via a content script injection. By doing so, developers gain the ability to monitor events within their modified XMLHttpRequest object while still maintaining the functionality of the original XMLHttpRequest object, allowing for seamless traffic monitoring without disrupting the user experience on third-party websites.
**Step-by-Step Guide to Overriding XMLHttpRequest
Create a Script.js**
This is an immediately invoked function expression (IIFE). It creates a private scope for the code inside, preventing variables from polluting the global scope.
XHR Prototype Modification: These lines save references to the original send and open methods of the XMLHttpRequest prototype.
Override Open Method: This code overrides the open method of XMLHttpRequest. When we create an XMLHttpRequest, this modification stores the request URL in the URL property of the XHR object.
Override Send Method: This code overrides the send method of XMLHttpRequest. It adds an event listener for the 'load' event. If the URL contains the specified string ("UserByScreenName"), it executes code to handle the response. After that, it calls the original send method.
Handling the Response: If the URL includes "UserByScreenName," it creates a new div element, sets its innerText to the intercepted response, and appends it to the document body.
Let's explore how we can override XMLHttpRequest!
Creating a Script Element: This code creates a new script element, sets its type to "text/javascript," specifies the source URL using Chrome.runtime.getURL("script.js"), and then appends it to the head of the document since it is a common way to inject a script into a web page.
Checking for DOM Elements: The checkForDOM function checks if the document's body and head elements are present. If they are, it calls the interceptData function. If not, it schedules another call to checkForDOM using requestIdleCallback to ensure the script waits until the necessary DOM elements are available.
Scraping Data from Profile: The scrapeDataProfile function looks for an element with the ID "__interceptedData." If found, it parses the JSON content of that element and logs it to the console as the API response. If not found, it schedules another call to scrapeDataProfile using requestIdleCallback.
Initiating the Process: These lines initiate the process by calling requestIdleCallback on checkForDOM and scrapeDataProfile. This ensures that the script begins by checking for the existence of the necessary DOM elements and then proceeds to scrape data when the "__interceptedData" element is available.
Pros
You can obtain substantial information from the server response and store details not in the user interface.
*Cons
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The server response may change after a certain period.
Here's a valuable tip
By simulating Twitter's internal API calls, you can retrieve additional information that wouldn't typically be displayed. For instance, you can access user details who liked tweets by invoking the API responsible for fetching this data, which is triggered when viewing the list of users who liked a tweet. However, it's important to keep these API calls straightforward, as overly frequent or unusual calls may trigger bot protection measures. This caution is crucial, as platforms like LinkedIn often use such strategies to detect scrapers, potentially leading to account restrictions or bans.
Conclusion
To conclude the entire situation, one must grasp the specific use case. Sometimes, extracting data from the user interface can be challenging due to its scattered placement. Therefore, opting to listen to API calls and retrieve data in a unified manner is more straightforward, especially for a browser extension development company aiming to streamline data extraction processes. Many websites utilize APIs to fetch collections of entities from the backend, subsequently binding them to the UI; this is precisely why intercepting API calls becomes essential.
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