What Is Hydration
Understand how hydration reuses server HTML.
Defining Hydration
Hydration is the process where the client-side Angular app reuses the server-rendered HTML, attaching event listeners and state to the existing DOM instead of throwing it away and rendering again.
Life Without Hydration
Legacy SSR used destructive hydration: the client wiped the server DOM and re-rendered from scratch. This caused a visible flicker and discarded the server's work.