transform-templated-string.js

function transformTemplatedString(template, replacements) {    
    return Object.entries(replacements).reduce((transformedString, [key, value]) => {
        if (!/^[a-z|_]+$/i.test(key)) {
            throw new Error('keys may only consist of letters and underscores');
        }
        
        const keyPattern = new RegExp(`%{${key}}`, 'g');
        return transformedString.replace(keyPattern, value);
    }, template);
}

transformTemplatedString(
  'Cannot have insurance score less than %{minimum_insurance_score} and insurance lapse of %{minimum_days_for_lapse} or more days',
  {minimum_insurance_score: '100', minimum_days_for_lapse: 5, foo: 'bar'}
)
// 'Cannot have insurance score less than 100 and insurance lapse of 5 or more days'