Summ With Arity

SummArity.js

const summ = function (...args) {
	let arity = 0;
	let storage = [];
	
	const isNumber = (el) => {
		return (this instanceof Number) || typeof el === 'number' && !Number.isNaN(el);
	};

	if (isNumber(this)) {
		arity = 0 + this;
	} else if (this instanceof Object) {

		if (
			typeof this.arity === 'number' &&
			!Number.isNaN(this.arity) &&
			this.arity > 0
		) {
			arity = this.arity;
		}

		if (Array.isArray(this.storage)) {
			storage = this.storage.slice();
		}

	}

	if (arity === 0) {
		return 0;
	}

	if (args.length) {
		args.forEach(el => {
			if (
				isNumber(el) &&
				storage.length < arity
			) {
				storage.push(el);
			}
		});
	}
	
	if (storage.length < arity) {
		return summ.bind({
			arity,
			storage
		});
	}

	const result = storage.reduce((acc, el) => {
		return acc + el;
	}, 0);
	
	return result;
};

sumArity5 = summ.call(5);

console.log('summ arity 5', sumArity5(1, 2, 3, 4, 5)); // 15
console.log('summ arity 5', sumArity5(2, 3, 4)(5, 6)); // 20
console.log('summ arity 5', sumArity5(3, 4)(5, 6)(7)); // 25
console.log('summ arity 5', sumArity5(4, 5)(6)(7, 8)); // 30
console.log('summ arity 5', sumArity5(5)(6)(7)(8)(9)); // 35

// summ arity 4
console.log('summ arity 4', summ.bind(4)(1, 2, 3)(4, 5)); // 10
console.log('defaults {arity : 5, storage: [1, 2, 3]}', summ.bind({
	arity: 5,
	storage: [1,2,3]
})(4, 5)); // 15