index.js

'use strict';
const mimicFn = require('mimic-fn');

const calledFunctions = new WeakMap();

const onetime = (function_, options = {}) => {
	if (typeof function_ !== 'function') {
		throw new TypeError('Expected a function');
	}

	let returnValue;
	let callCount = 0;
	const functionName = function_.displayName || function_.name || '<anonymous>';

	const onetime = function (...arguments_) {
		calledFunctions.set(onetime, ++callCount);

		if (callCount === 1) {
			returnValue = function_.apply(this, arguments_);
			function_ = null;
		} else if (options.throw === true) {
			throw new Error(`Function \`${functionName}\` can only be called once`);
		}

		return returnValue;
	};

	mimicFn(onetime, function_);
	calledFunctions.set(onetime, callCount);

	return onetime;
};

module.exports = onetime;
// TODO: Remove this for the next major release
module.exports.default = onetime;

module.exports.callCount = function_ => {
	if (!calledFunctions.has(function_)) {
		throw new Error(`The given function \`${function_.name}\` is not wrapped by the \`onetime\` package`);
	}

	return calledFunctions.get(function_);
};