Tagged template literals that throw

safe.js

function ordinal(number) {
    const englishOrdinalRules = new Intl.PluralRules("en", { type: "ordinal" });
    const suffixes = {
        one: "st",
        two: "nd",
        few: "rd",
        other: "th"
    };
    
    const suffix = suffixes[englishOrdinalRules.select(number)];
    
    return `${number}${suffix}`;
}

function safe(strings, ...values) {
  const unsafeIndex = values.findIndex((value) => Number.isNaN(value) || value === undefined || value === null)
  if (unsafeIndex !== undefined) {
    throw new Error(`The ${ordinal(unsafeIndex)} value passed into the literal safe\`${strings.flatMap((string, index) => [string, index === unsafeIndex ? `\${${unsafeIndex}}`: values[index]]).join('')}\` was not allowed as it is: ${values[unsafeIndex]}`);
  }

  return strings.flatMap((string, index) => [string, values[index]]).join('');
}

It would also be nice to have a tagged template literal that can handle prefixing numeric values with ~ if they are approximate due to value >= Number.MAX_SAFE_INTEGER || value <= Number.MIN_SAFE_INTEGER and that could apply NumberFormat options using value.toLocaleString.

Maybe a way of passing in a shape like { numberFormatter: 'currency', value: number } for the correct formatters to be used for each data type (allowing this to be typed from a generic createFormattingTag function)?

Calculations on data with problems can be unsafe. We should look into ways of fixing that, too.