An AngularJS screen can look simple and still contain years of business rules. A save button may check permissions, normalize a date, update a draft and send the user back to a filtered list. Rebuilding the visible form in React leaves those rules easy to miss. Start the migration by recording what users can do and what the system writes. Move a complete workflow before counting converted components.
Set the scope before choosing a bridge
The official AngularJS support page states that support ended as of January 2022. An existing application may keep running, but that support status should be part of the team's dependency review. Check any separate extended support arrangement on its own terms. Do not confuse continued operation with an actively supported upstream project.
Define why the team is moving to React and what must stay unchanged. List the workflows in scope, the supported users and the backend contracts they rely on. Keep a redesign separate unless it is essential to the migration. Changing the framework, permissions and business process together makes a failed acceptance test harder to diagnose.
Choose a first slice with useful business coverage and a manageable boundary. A self-contained settings page can be a better pilot than a shared navigation bar used everywhere. Include a read, an edit and a failure path so the pilot tests more than rendering. Record which surrounding AngularJS pages must continue to work.
Choose route ownership or component ownership
React documents two ways to join an existing website. It can serve an entire subroute through server or proxy configuration, or render components into specific places on an existing page. Both are possible starting points. Neither chooses the boundary for your application's routing, session state or release process.
| Migration boundary | Useful when | Work to make explicit |
|---|---|---|
| Separate subroute | A workflow can own its pages | Routing, base path, direct loads and session handling |
| Dedicated DOM container | A small feature has clear inputs | Mounting, events, data transfer and cleanup |
| Whole application cutover | The remaining scope is already proven | Complete journey coverage and release recovery |
For a subroute, agree which server or proxy sends requests to the new application. Test a direct page load as well as navigation from the old screen. For a component, write down the values it receives and the events it sends back. Avoid a bridge that exposes the entire old application as an undocumented global dependency.
Give React its own DOM container
React's createRoot creates a root inside a browser DOM node. Calling root.render displays the component there, and React takes over the DOM inside the root. The first render clears existing HTML within that container. Choose an element reserved for React rather than placing it over content that the old application still expects to control.
React also documents root.unmount for cases where other code removes the root or an ancestor. Connect cleanup to the lifecycle of your integration. Test entering and leaving the old route repeatedly. The React tree should not keep subscriptions or event handlers alive after its host screen disappears.
If the target container already holds HTML generated by React on the server or during a build, React documents hydrateRoot instead of createRoot. That is a separate case from placing a new client-rendered component inside an AngularJS page. Choose the API based on how that container's HTML was produced.
Move state through explicit contracts
Inventory the values the workflow reads, changes and saves. Include current user permissions, selected account, filters, unsaved form data and server responses. Decide which side owns each value while the two implementations coexist. A shared value with two writers needs an explicit conflict rule, not an assumption that both screens will stay synchronized.
Prefer a small adapter around the existing backend calls. Record request fields, response shapes, empty states and error handling before changing them. Keep authentication and authorization checks intact. A hidden button is not a replacement for a server-side permission check. Test the same allowed and denied actions through the new workflow.
Handle changes from the React side as explicit events or operations in the bridge. Confirm that the surrounding application observes the update through its own integration path. Do not depend on an accidental page refresh to make saved data appear. Document who owns loading indicators, error messages and cancellation.
Capture behavior before translating the screen
Use the existing application as a source of examples, then confirm expected behavior with an operator. Old behavior can contain defects too. Mark an intentional correction separately so a reviewer can distinguish a migration regression from an approved change. Our AI-assisted legacy code migration guide covers this distinction more broadly.
- Open a saved record from a direct link and from a filtered list.
- Change a field, cancel and confirm nothing was saved.
- Save valid and invalid input and inspect the resulting data.
- Repeat with a user who lacks edit permission.
- Test expired sessions, failed requests and a retry after a slow response.
- Check keyboard navigation, focus and messages that explain errors.
Compare the written records as well as the visible page. Check dates, empty values and relationships using representative data. A screen can look correct while saving a different value. Keep a repeatable acceptance checklist with the test inputs and expected outcome.
Use AI on bounded pieces of the migration
An AI assistant can propose a dependency inventory, draft a component or suggest tests from a written behavior description. Give it a bounded task and inspect the output. Do not accept a new library, changed API field or removed permission check just because the generated page builds.
Keep the reviewed behavior description separate from the generated implementation. Run tests against both normal and failure paths. Ask reviewers to identify assumptions the code introduces, especially defaults for missing data. Compilation shows that the code can be built. It does not establish that the old workflow has been preserved.
Roll out with a working recovery path
Release the first slice behind a route switch or another controlled selection mechanism suited to the application. Monitor failed requests, duplicate actions and user reports for that workflow. Define when to switch users back and rehearse the switch before depending on it.
Make sure recovery still works after the new code has saved data. If a backend change makes old clients incompatible, a frontend switch alone cannot restore the previous behavior. Keep database changes out of the pilot where possible. If data must change, plan that separately through the data migration process.
Retire old routes and bridge code only after their callers are identified and the new workflow is accepted. Remove unused assets and dependencies as an explicit cleanup step. Otherwise, the team may finish the visible React work while still carrying the original application in every release.
How Remqa helps with AngularJS migrations
Remqa provides engineering support for code migrations and customer-facing implementation work. We can help map workflow boundaries, build a pilot and define acceptance checks before a wider rollout. Bring one difficult route, its API calls and the behavior your operators need to preserve. Explore code migration or walk an engineer through the application.