index.js

function debounce(function_, wait = 100, options = {}) {
	if (typeof function_ !== 'function') {
		throw new TypeError(`Expected the first parameter to be a function, got \`${typeof function_}\`.`);
	}

	if (wait < 0) {
		throw new RangeError('`wait` must not be negative.');
	}

	// TODO: Deprecate the boolean parameter at some point.
	const {immediate} = typeof options === 'boolean' ? {immediate: options} : options;

	let storedContext;
	let storedArguments;
	let timeoutId;
	let timestamp;
	let result;

	function run() {
		const callContext = storedContext;
		const callArguments = storedArguments;
		storedContext = undefined;
		storedArguments = undefined;
		result = function_.apply(callContext, callArguments);
		return result;
	}

	function later() {
		const last = Date.now() - timestamp;

		if (last < wait && last >= 0) {
			timeoutId = setTimeout(later, wait - last);
		} else {
			timeoutId = undefined;

			if (!immediate) {
				result = run();
			}
		}
	}

	const debounced = function (...arguments_) {
		if (
			storedContext
			&& this !== storedContext
			&& Object.getPrototypeOf(this) === Object.getPrototypeOf(storedContext)
		) {
			throw new Error('Debounced method called with different contexts of the same prototype.');
		}

		storedContext = this; // eslint-disable-line unicorn/no-this-assignment
		storedArguments = arguments_;
		timestamp = Date.now();

		const callNow = immediate && !timeoutId;

		if (!timeoutId) {
			timeoutId = setTimeout(later, wait);
		}

		if (callNow) {
			result = run();
		}

		return result;
	};

	Object.defineProperty(debounced, 'isPending', {
		get() {
			return timeoutId !== undefined;
		},
	});

	debounced.clear = () => {
		if (!timeoutId) {
			return;
		}

		clearTimeout(timeoutId);
		timeoutId = undefined;
	};

	debounced.flush = () => {
		if (!timeoutId) {
			return;
		}

		debounced.trigger();
	};

	debounced.trigger = () => {
		result = run();

		debounced.clear();
	};

	return debounced;
}

// Adds compatibility for ES modules
module.exports.debounce = debounce;

module.exports = debounce;