Created Injecting code to UT Pages (markdown)

Injecting-code-to-UT-Pages.md

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+# Code Injection Guide
+
+This page documents how we inject code into supported pages across the UT Austin web ecosystem.
+
+# Choosing a page to inject on
+Current URL is obtained through `window.location.href`
+
+## siteSupport
+Contains enum to determine what page a user is on. For example
+```ts
+if (url.includes('my.utexas.edu/student/student/index') || url.includes('my.utexas.edu/student/')) {
+    return SiteSupport.MY_UT;
+}
+```
+
+## renderComponent
+Found in `index.tsx`, the `renderComponent` function is a utility used by the extension to inject React components into websites (and other supported pages). It creates a new div and appends it to the document body. It then uses React’s createRoot to render the React component inside this container.
+
+```ts
+const renderComponent = (Component: React.ComponentType) => {
+    const container = document.createElement('div');
+    container.id = 'extension-root';
+    document.body.appendChild(container);
+
+    createRoot(container).render(
+        <React.StrictMode>
+            <Component />
+        </React.StrictMode>
+    );
+};
+```
+
+After a site is determined, components are rendered in `index.tsx`. For example
+
+```ts
+if (support === SiteSupport.COURSE_CATALOG_DETAILS || support === SiteSupport.COURSE_CATALOG_LIST) {
+    renderComponent(() => <CourseCatalogMain support={support} />);
+}
+
+if (support === SiteSupport.MY_UT) {
+    renderComponent(InjectedButton);
+}
+
+if (support === SiteSupport.COURSE_CATALOG_SEARCH) {
+    renderComponent(DaysCheckbox);
+}
+```
+
+# Examples
+
+## CourseCatalogMain
+
+Relevant page:
+![image](https://github.com/user-attachments/assets/21645b97-8b8e-46db-b756-12c3d7fc870a)
+
+`<ExtensionRoot>` used to prevent the native page styles from being overridden with our own. 
+
+```ts
+return (
+        <ExtensionRoot>
+            <NewSearchLink />
+            <RecruitmentBanner />
+            <TableHead>Plus</TableHead>
+            {rows.map(
+                row =>
+                    row.course && (
+                        <TableRow
+                            key={row.course.uniqueId}
+                            row={row}
+                            isSelected={row.course.uniqueId === selectedCourse?.uniqueId}
+                            activeSchedule={activeSchedule}
+                            onClick={handleRowButtonClick(row.course)}
+                        />
+                    )
+            )}
+            <CourseCatalogInjectedPopup
+                course={selectedCourse!} // always defined when showPopup is true
+                show={showPopup}
+                onClose={() => setShowPopup(false)}
+                afterLeave={() => setSelectedCourse(null)}
+            />
+            {enableScrollToLoad && <AutoLoad addRows={addRows} />}
+        </ExtensionRoot>
+    );
+```