Typesafe Singular/Plural String Builder function

singularPluralStringBuilder.ts

type SingularPluralSignature = {
    length: number;
    singular: string;
    plural: string;
    ifLengthZero?: string;
};

const buildSingularPluralString = (...args: Array<string | SingularPluralSignature>) =>
    args.reduce((acc, next) =>
        typeof next === 'string' ? [
            ...acc,
            next
        ] : [
            ...acc,
            ...(next.length > 1 ? [
                next.plural
            ] : [
                next.length === 0 && next?.ifLengthZero ? next.ifLengthZero : next.singular
            ])
        ], [] as string[]).join('')

const numberDevs = 2;

const builtString = buildSingularPluralString('Oie, ', {
    length: numberDevs,
    ifLengthZero: 'não temos devs',
    singular: 'eu sou um dev',
    plural: `nós somos ${numberDevs} devs`
}, '!')

console.log(builtString);

type SingularPluralSignature = {
  length: number;
  singular: string;
  plural: string;
};

const buildSingularPluralString = (
  ...args: Array<string | SingularPluralSignature>
) => {
  const words = args.reduce((acc, next) => {
    const isString = typeof next === "string";

    const phase: string[] = [...acc];

    if (isString) {
      phase.push(next);
    }

    const isPlural = next.length > 1;
    if (!isString && isPlural) {
      return [next.plural];
    }

    if (!isString && !isPlural) {
      return [next.singular];
    }

    return phase;
  }, [] as string[]);

  const phase = words.join("");
  return phase;
};

// Test
const numberDevs = 2;

const builtString = buildSingularPluralString(
  "Oie, ",
  {
    length: numberDevs,
    singular: "eu sou um dev",
    plural: `nós somos ${numberDevs} devs`,
  },
  "!",
);

console.log(builtString);