typescript narrow type on throw

const SALT_ROUNDS = process.env.SALT_ROUNDS;

if (!SALT_ROUNDS) throw new Error("salt rounds not specified for bcrypt");

export { SALT_ROUNDS}

const SALT_ROUNDS = process.env.SALT_ROUNDS;

if (!SALT_ROUNDS) throw new Error("salt rounds not specified for bcrypt");

export { SALT_ROUNDS}

function assertTruthy (
    param: unknown,
    envName: string
): asserts param is string {
    if (!param) throw new Error(`${envName} is not provided`);
    else return;
}

assertTruthy(SALT_ROUNDS, "SALT_ROUNDS");

function assertTruthy (
    param: unknown,
    envName: string
): asserts param is string {
    if (!param) throw new Error(`${envName} is not provided`);
    else return;
}

assertTruthy(SALT_ROUNDS, "SALT_ROUNDS");