beaverjs/dist/BaseEventHandler.js

An abstraction around WebExtension messaging

export class BaseEventHandler {
    constructor() {
        this.eventMap = new Map();
        queueMicrotask(() => this.setup());
    }
    insertEvent(key, eventHandler) {
        // all the "as ..." are necessary because Typescript doesn't like inserting EventMap[K] into EventMap[keyof EventMap]
        // even though K extends keyof EventMap. This is probably due to the definition of `eventMap`
        if (this.eventMap.has(key)) {
            const entry = this.eventMap.get(key);
            if (Array.isArray(entry)) {
                // 2 or more entries
                entry.push(eventHandler);
            }
            else {
                // only one entry
                this.eventMap.set(key, [
                    entry,
                    eventHandler,
                ]);
            }
        }
        else {
            this.eventMap.set(key, eventHandler);
        }
    }
    on(key, fn) {
        this.insertEvent(key, fn);
        return this;
    }
    once(key, fn) {
        this.insertEvent(key, { fn, once: true });
        return this;
    }
    emit(key, data, ...args) {
        const serialized = this.serialize(key, data);
        this.sendEvent(serialized, ...args);
    }
    handleEvent(key, data, sender) {
        const entry = this.eventMap.get(key);
        if (!entry)
            return;
        if (typeof entry === 'function') {
            // "fast path" - no cleanup or anything
            entry(data, sender);
            return;
        }
        if (Array.isArray(entry)) {
            const result = entry.filter(value => {
                if (typeof value === 'function') {
                    value(data, sender);
                    return true;
                }
                value.fn(data, sender);
                return value.once;
            });
            if (result.length === 0)
                this.eventMap.delete(key);
            else if (result.length === 1)
                this.eventMap.set(key, result[0]);
            else
                this.eventMap.set(key, result);
        }
        else {
            if (entry.once)
                this.eventMap.delete(key);
            entry.fn(data, sender);
        }
    }
    handleSerialized(serialized, sender) {
        const deserialized = this.deserialize(serialized);
        // another function for better type checking
        this.handleEvent(deserialized.type, deserialized.data, sender);
    }
}
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