wp-calypso/client/my-sites/stats/components/highlight-cards/lib/numbers.ts

import { formatNumber as formatNumberI18n } from '@automattic/number-formatters';

export function formatNumber( number: number | null, isShortened = true, showSign = false ) {
	const numberFormatOptions: Intl.NumberFormatOptions = isShortened
		? {
				notation: 'compact',
				maximumFractionDigits: 1,
				...( showSign && { signDisplay: 'exceptZero' } ),
		  }
		: { notation: 'standard', ...( showSign && { signDisplay: 'exceptZero' } ) };

	return number !== null ? formatNumberI18n( number, { numberFormatOptions } ) : '-';
}

export function formatPercentage(
	number: number | null,
	usePreciseSmallPercentages: boolean = false
) {
	// If the number is < 1%, then use 2 significant digits and maximumFractionDigits of 2.
	// Otherwise, use the default percentage formatting options.
	const numberFormatOptions: Intl.NumberFormatOptions =
		usePreciseSmallPercentages && number && number < 0.01
			? { style: 'percent', maximumFractionDigits: 2, maximumSignificantDigits: 2 }
			: { style: 'percent' };
	return number !== null ? formatNumberI18n( number, { numberFormatOptions } ) : '-';
}

export function subtract( a: number | null, b: number | null | undefined ): number | null {
	return a === null || b === null || b === undefined ? null : a - b;
}

export function percentCalculator( part: number | null, whole: number | null | undefined ) {
	if ( part === null || whole === null || whole === undefined ) {
		return null;
	}
	// Handle NaN case.
	if ( part === 0 && whole === 0 ) {
		return 0;
	}
	const answer = part / whole;
	// Handle Infinities as 100%.
	return ! Number.isFinite( answer ) ? 1 : answer;
}