Some tips to get started with the UI development:
If you're looking for an IDE to write the TypeScript code, Visual Studio Code works well out of the box. WebStorm or IntelliJ Idea Ultimate (Community does not have JavaScript/TypeScript support) also work really well. The code is located in the ui folder.
See Build Instructions page for the details about starting the local development server.
The devserver has a live reload functionality: once you make a change in TypeScript files, the resulting code will be recompiled and the page is going to reload automatically. By default, this logic uses a timeout in order to prevent successive reloads on rapid changes. This logic can be disabled via development-only “Rapid live reload” flag in the UI. Disabling it will reload the page earlier, at the cost of sometimes making multiple reloads in a row.
Perfetto UI uses the Mithril library for rendering the interface. The majority of the components in the codebase use class components. When Mithril is imported via m alias (as it is usually done in the codebase), the class component should extend m.ClassComponent, which has an optional generic parameter allowing the component to take inputs. The entry point of class components is a view method, returning a tree of virtual DOM elements to be rendered when the component is present on the page.
Local state of components can reside in class members and accessed directly in methods via accessing this. State that is shared across different components is stored in the State class definition, and should be modified via implementing a new action in src/common/actions.ts. A new field added to State should be initialized in src/common/empty_state.ts.
There are restrictions on whan can be used in the global state: plain JS objects are OK, but class instances are not (this limitation is due to state serialization: the state should be a valid JSON object). If storing class instances (like Map and Set data structures) is necessary, these can be stored in the NonSerializableState portion of the state, that is omitted from saving into JSON objects.