env.esq/src/utils/ViewModel.js

/*
Copyright 2020 The Matrix.org Foundation C.I.C.

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/

class EventEmitter {
    constructor() {
        this._handlersByName = {};
    }

    emit(name, ...values) {
        const handlers = this._handlersByName[name];
        if (handlers) {
            for(const h of handlers) {
                h(...values);
            }
        }
    }

    on(name, callback) {
        let handlers = this._handlersByName[name];
        if (!handlers) {
            this._handlersByName[name] = handlers = new Set();
        }
        handlers.add(callback);
        return () => {
            this.off(name, callback);
        }
    }

    off(name, callback) {
        const handlers = this._handlersByName[name];
        if (handlers) {
            handlers.delete(callback);
            if (handlers.length === 0) {
                delete this._handlersByName[name];
            }
        }
    }
}

export class ViewModel extends EventEmitter {
    constructor(options) {
        super();
        this._options = options;
    }

    emitChange() {
        this.emit("change");
    }

    get request() { return this._options.request; }
    get origin() { return this._options.origin; }
    get openLink() { return this._options.openLink; }
    get platforms() { return this._options.platforms; }
    get preferences() { return this._options.preferences; }

    childOptions(options = {}) {
        return Object.assign({
            request: this.request,
            origin: this.origin,
            openLink: this.openLink,
            platforms: this.platforms,
            preferences: this.preferences,
        }, options);
    }
}