Format with Intl

Create a function to format amount with Intl native api

// number
interface NumberFormatOptions {
  currencyDisplay?: Intl.NumberFormatOptions["currencyDisplay"];
  style?: Intl.NumberFormatOptions["style"];
  currency?: Intl.NumberFormatOptions["currency"];
  locale?: string;
}
export function formatAmount(amount: string, options?: NumberFormatOptions) {
  const { currency = "USD", currencyDisplay = "narrowSymbol", style = "currency", locale = undefined } = options || {};

  const amountFloat = parseFloat(amount);
  if (isNaN(amountFloat)) {
    throw new Error(`Invalid amount: "${amount}"`);
  }

  const formatter = new Intl.NumberFormat(locale, {
    style,
    currency,
    currencyDisplay,
  });

  return formatter.format(amountFloat);
}

export const numberFormat = new Intl.NumberFormat("en-US", {
  notation: "compact",
});

export const timeFormatter = new Intl.RelativeTimeFormat("en-US", {
  style: "long",
});

// number.test.ts
import { formatAmount } from "./number";

describe("formatAmount", () => {
  it("should format amount with default options", () => {
    const amount = "123.45";
    const result = formatAmount(amount);
    expect(result).toBe("$123.45");
  });

  it("should format amount with custom currency", () => {
    const amount = "123.45";
    const options = { currency: "EUR" };
    const result = formatAmount(amount, options);
    expect(result).toBe("€123.45");
  });

  it("should format amount with custom currency display", () => {
    const amount = "123.45";
    const result = formatAmount(amount, { currencyDisplay: "symbol" });
    expect(result).toBe("$123.45");
  });

  it("should format amount with custom style", () => {
    const amount = "123.45";
    const result = formatAmount(amount, { style: "decimal" });
    expect(result).toBe("123.45");
  });

  it("should throw an error with invalid amount", () => {
    const amount = "abc";
    expect(() => formatAmount(amount)).toThrowError();
  });

  it("should not throw an error with missing options", () => {
    const amount = "123.45";
    expect(() => formatAmount(amount)).not.toThrowError();
  });
});