Carbon/src/js/events/membership.js

const {simpleEvent} = require("./event")

const UnknownMembership = simpleEvent((e) => e.type == "m.room.member", (e) => "unknown membership event")

function createMembershipEvent(membership, message) {
	return simpleEvent((e) => e.type == "m.room.member" && e.content.membership === membership, message)
}

const JoinedEvent = createMembershipEvent("join", (e) => "joined the room")
const InvitedEvent = createMembershipEvent("invite", (e) => `invited ${e.content.displayname} the room`)
const LeaveEvent = createMembershipEvent("leave", () => "left the room")

module.exports = [JoinedEvent, InvitedEvent, LeaveEvent, UnknownMembership]