Radix.js

function floorMod(a, b) {
	return a - b * Math.floor(a / b);
}

function toRadix(decimal, base) {
	let array = [];
	do array.unshift(floorMod(decimal, base));
	while ((decimal = Math.floor(decimal / base)) !== 0);
	return array;
}

function toDecimal(radix, base) {
	return radix.reverse().reduce((acc, cur, i, arr) => acc + cur * base ** i);
}

console.log(toRadix(-15, -2))
console.log(toDecimal([ 4, 3, 7 ], -10))