exercism-ts/all-your-base/all-your-base.ts

export function convert(
    digits: number[],
    inputBase: number,
    outputBase: number
): number[] {
    if (inputBase < 2) {
        throw new Error("Wrong input base")
    }
    if (outputBase < 2) {
        throw new Error("Wrong output base")
    }
    if (outputBase !== Math.floor(outputBase)) {
        throw new Error("Wrong output base")
    }
    if (inputBase === outputBase) {
        return digits;
    }
    if (digits.length == 0) {
        throw new Error("Input has wrong format");
    }
    if (digits[0] === 0 && digits.length > 1) {
        throw new Error("Input has wrong format");
    }
    let reversed = [...digits];
    reversed.reverse();
    let value = 0;
    let pow = 1;

    for (const digit of reversed) {
        if (digit < 0 || digit >= inputBase) {
            throw new Error("Input has wrong format");
        }
        value += digit * pow;
        pow *= inputBase;
    }
    reversed = [];
    let current = value;
    for (; ;) {
        reversed.push(current % outputBase);
        current = Math.floor(current / outputBase);
        if (current === 0) {
            break;
        }
    }
    const out = [...reversed];
    out.reverse();
    return out;
}