What they are and what they can do.
WHAT AN EXTENSION IS
A package of web technologies that modifies or extends the browser.
WHAT THEY CAN DO
Modify pages Add interface elements to the browser Intercept and observe requests Store data Communicate with servers React to browser events
WHAT THE COMPONENTS ARE
A manifest, declaring what the extension is and requires A background service worker, for events and logic Content scripts, running within pages
Interface pages: popups, options, side panels
WHAT THE MANIFEST DECLARES
Permissions Which pages content scripts run on Entry points The extension's identity and version
WHAT THE CURRENT PLATFORM VERSION CHANGED
Background pages replaced by service workers, which terminate when idle Remotely hosted code prohibited Request handling changed to declarative rules
WHY THOSE CHANGES MATTER
State cannot be held in memory between events, and behaviour must be declared rather than executed.
WHAT TO ESTABLISH BEFORE BUILDING
Whether what you need is possible under the current rules.
