pricing_template_tag.js

function pricing(literals, ...replacements) {
  // Initialize the final string
  let finalString = '';
  
  for (let i = 0; i < replacements.length; i++) {
    // Get the current literal and replacement
    const literal = literals[i];
    const replacement = replacements[i];
    
    // Trim trailing whitespaces from the current literal
    const trimmed = literal.trimRight();
    const length = trimmed.length;
    
    // Check if current replacement is a number
    const isNumber = typeof replacement === 'number';
    
    // Check if current literal string ends with $
    const isPrice = /\$$/.test(trimmed);
    
    // Check if number is followed by literal that ends with $
    // and use the desired formatting
    finalString += (isNumber && isPrice)
      ? `${trimmed.substr(0, length - 1).trimRight()} USD ${replacement.toFixed(2)}`
      : `${literal}${replacement}`;
  }
  
  // Attach the last literal to the final string
  return finalString + literals[literals.length - 1];
}