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Tooling · medium

35. Internationalization

Formatting numbers, currency and dates for a global audience.

1 min read3 questionsup to 50 XPtopic 35/50

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`Intl` is available in modern React Native and is the right tool for formatting currency, numbers and dates correctly per locale, rather than hand-rolling string concatenation.

function formatUsd(amount: number, locale = "en-US") {
  return new Intl.NumberFormat(locale, { style: "currency", currency: "USD" }).format(amount);
}

formatUsd(1234.5); // "$1,234.50"

Token amounts often need custom formatting beyond `Intl` (e.g. showing 18-decimal precision truncated sensibly), so a dedicated `formatTokenAmount` helper alongside `Intl` is common.

How to study this topic

  1. 1. Read the explanation once end to end, skipping the code.
  2. 2. Re-read the code snippets and say out loud what each line does.
  3. 3. Answer the quiz without scrolling back — that is the real check.
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Check your understanding

  1. 1. What built-in API formats currency per locale?

  2. 2. Why might token amounts need custom formatting beyond Intl?

  3. 3. What locale-aware behavior does Intl handle well?

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