add.js

function add(val = 0, ...args) {
	let sum = args.reduce((prev, curr) => {
		return prev + curr;
	}, val);
	let ret = add.bind(this, sum);
	ret.value = () => sum;
	ret.add = ret;
	return ret;
}

console.log(add(1, 2).value() === 3);
console.log(add(1, 2)(3).value() === 6);
console.log(add(2, 3, 4)(5)(4, 6).value() === 24); 
console.log(add(2, 3, 4)(5).add(4,6).value() + 5 === 29);