Created Detecting changes in HTML page sources (markdown)

Detecting-changes-in-HTML-page-sources.md

@@ -0,0 +1,10 @@
+For some webpages, relevant information is best accessed by checking the HTML page source.
+
+## Use Case
+For example, the HTML response of web shops like https://www.campuspoint.de contains the product listings in JSON format which is then processed client-side with JS to produce the final markup. One could use the JS-enabled [[Playwright-content-fetcher]] for such a webpage, but checking against the page source is more efficient.
+
+## Approach
+* In the General tab, prepend the target URL with `source:` (example: `source:https://www.campuspoint.de/mobile/notebooks/lenovo/thinkpad-t-serie/thinkpad-t14s.html`)
+* In the Request tab, choose the "Basic fast Plaintext/HTTP Client" fetch method
+* Choose a suitable trigger in the Filters & Triggers tab, for example the regex-based "Extract text" one.
+  * Example: use `/"product_count":(\d+)/i` to check when campuspoint.de adds new models of a certain laptop series to their inventory.