sendMessage()

sendMessage(messageId: string, data: any, destination: string)

Sends a message to some other part of your extension.

• If there is no listener on the other side an error will be thrown where sendMessage was called.
• Listener on the other may want to reply. Get the reply by awaiting the returned Promise
• An error thrown in listener callback (in the destination context) will behave as usual, that is, bubble up, but the same error will also be thrown where sendMessage was called
• If the listener receives the message but the destination disconnects (tab closure for exmaple) before responding, sendMessage will throw an error in the sender context.

messageId

Required | string

Any string that both sides of your extension agree on. Could be get-flag-count or getFlagCount or GET_FLAG_COUNT, as long as it's same on receiver's onMessage listener.

data

Required | any

Any serializable value you want to pass to other side, latter can access this value by refering to data property of first argument to onMessage callback function.

destination

Required | string

The actual identifier of other endpoint.

Example: devtools or content-script or background or content-script@133 or devtools@453

content-script, window and devtools destinations can be suffixed with @<tabId> to target specific tab. Example: devtools@351, points to devtools panel inspecting tab with id 351.

For content-script, a specific frameId can be specified by appending the frameId to the suffix @<tabId>.<frameId>.

Read Notes section to see how destinations (or endpoints) are treated.