decorators.ts

/*---------------------------------------------------------------------------------------------
 *  Copyright (c) Microsoft Corporation. All rights reserved.
 *  Licensed under the MIT License. See License.txt in the project root for license information.
 *--------------------------------------------------------------------------------------------*/

import { done } from './util';

function decorate(decorator: (fn: Function, key: string) => Function): Function {
	return (_target: any, key: string, descriptor: PropertyDescriptor): void => {
		if (typeof descriptor.value === 'function') {
			descriptor.value = decorator(descriptor.value, key);
		} else if (typeof descriptor.get === 'function') {
			descriptor.get = decorator(descriptor.get, key) as () => any;
		} else {
			throw new Error('not supported');
		}
	};
}

function _memoize(fn: Function, key: string): Function {
	const memoizeKey = `$memoize$${key}`;

	return function (this: any, ...args: any[]) {
		if (!this.hasOwnProperty(memoizeKey)) {
			Object.defineProperty(this, memoizeKey, {
				configurable: false,
				enumerable: false,
				writable: false,
				value: fn.apply(this, args)
			});
		}

		return this[memoizeKey];
	};
}

export const memoize = decorate(_memoize);

function _throttle<T>(fn: Function, key: string): Function {
	const currentKey = `$throttle$current$${key}`;
	const nextKey = `$throttle$next$${key}`;

	const trigger = function (this: any, ...args: any[]) {
		if (this[nextKey]) {
			return this[nextKey];
		}

		if (this[currentKey]) {
			this[nextKey] = done(this[currentKey]).then(() => {
				this[nextKey] = undefined;
				return trigger.apply(this, args);
			});

			return this[nextKey];
		}

		this[currentKey] = fn.apply(this, args) as Promise<T>;

		const clear = () => this[currentKey] = undefined;
		done(this[currentKey]).then(clear, clear);

		return this[currentKey];
	};

	return trigger;
}

export const throttle = decorate(_throttle);

function _sequentialize(fn: Function, key: string): Function {
	const currentKey = `__$sequence$${key}`;

	return function (this: any, ...args: any[]) {
		const currentPromise = this[currentKey] as Promise<any> || Promise.resolve(null);
		const run = async () => await fn.apply(this, args);
		this[currentKey] = currentPromise.then(run, run);
		return this[currentKey];
	};
}

export const sequentialize = decorate(_sequentialize);

export function debounce(delay: number): Function {
	return decorate((fn, key) => {
		const timerKey = `$debounce$${key}`;

		return function (this: any, ...args: any[]) {
			clearTimeout(this[timerKey]);
			this[timerKey] = setTimeout(() => fn.apply(this, args), delay);
		};
	}) as MethodDecorator;
}