Function for formatting decimal numbers, including specifying decimal places and optionally applying localization.

format-decimals.js

/*
	Function for formatting decimal numbers,
	including specifying decimal places and
	optionally applying localization.

	Parameters:
		n: (Number | String)
			Number to be formatted.
		
		decimals: (Number)
			Maximum number of decimal places.
		
		forceDecimals: (Boolean, optional)
			Pad number with zeros to meet the
			requested number of decimal places.
		
		locale: (String | Boolean, optional)
			If a string, it specifies a
			locale to apply to the result.

			If 'true', use the default system locale.

			If undefined or false, no localization
			will be performed on the result.
*/
function formatDecimals(n, decimals, forceDecimals, locale) {
	if (forceDecimals === undefined)
		forceDecimals = false;
	
	if (typeof n !== "number")
		n = parseFloat(n);
	
	// If NaN
	if (n !== n)
		n = 0;

	if (locale !== undefined && locale !== false) {
		locale = locale === true ? undefined : locale;

		if (forceDecimals)
			return n.toLocaleString(locale, {
				minimumFractionDigits: decimals,
				maximumFractionDigits: decimals
			});
		else
			return n.toLocaleString(locale, {
				minimumFractionDigits: decimals
			});
	} else {
		const r = n.toFixed(decimals);
		return forceDecimals ? r : parseFloat(r).toString();
	}
}