Playing around with string templates in JS (for validation)

validations.js

const isArray = (o) => o.map !== undefined;

const generateValidation = (string, ...validationLiterals) => {
  const [ head, ...strings ] = isArray(string) ? string : [string];

  return (...validationArg) => {
    const validationResults = validationLiterals.map((validation) => validation(...validationArg));
    if (validationResults.every((e) => e === null)) {
      return { valid: true };
    }

    return { valid: false, message: strings.reduce((ac, s, i) => {
        return `${ac}${validationResults[ i ]}${s}`
      }, head)};
  };
};

const isNotEmpty = generateValidation`Value of '${(value, field) => value !== '' ? null : field}' cannot be empty`;

const hasDuplicates = (array) =>  new Set(array).size !== array.length;
const findDuplicates = (array) => new Set(array.filter((e, i) => array.indexOf(e, i+1) !== -1));

const filterUnderLimit = (limit, head, rest) => rest.reduce((acc, duplicate) => {
  if ([...acc, duplicate].join(', ').length > limit) { return acc; }
  return [...acc, duplicate];
}, [ head ]);

const wrapValues = (char, array) => array.map((e) => `${char}${e}${char}`);

const areDuplicatesInKeywords = (limit) => (array) => {
  if (!hasDuplicates(array)) { return null; }

  const [ head, ...rest ] = findDuplicates(array);
  if (head.length > limit) { return ''; }

  const duplicates = filterUnderLimit(limit, head, rest);

  if (duplicates.length < rest.length + 1) { return `: ${ wrapValues('\'', duplicates).join(', ') }...` }
  return `: ${ wrapValues('\'', duplicates).join(', ') }`;
};

const noDuplicateKeywords = generateValidation`Keywords cannot contains duplicates${areDuplicatesInKeywords(12)}`;
const normalNoDuplicateKeywords = generateValidation('Keyword duplicates are not allowed', areDuplicatesInKeywords(12));

console.log(isNotEmpty("something", "Campaign Name"));
console.log(isNotEmpty("", "Campaign Name"));

console.log(noDuplicateKeywords(['something']));
console.log(noDuplicateKeywords(['something', 'cool', 'something', 'awesome', 'cool', 'a' , 'a']));
console.log(noDuplicateKeywords(['something', 'cool', 'cool']));
console.log(noDuplicateKeywords(['something', 'something', 'awesome', 'cool']));
console.log(noDuplicateKeywords(['somethingawesomeandcool', 'something', 'somethingawesomeandcool', 'cool']));

console.log(normalNoDuplicateKeywords(['something']));
console.log(normalNoDuplicateKeywords(['something', 'cool', 'something', 'awesome', 'cool', 'a' , 'a']));
console.log(normalNoDuplicateKeywords(['something', 'cool', 'cool']));
console.log(normalNoDuplicateKeywords(['something', 'something', 'awesome', 'cool']));
console.log(normalNoDuplicateKeywords(['somethingawesomeandcool', 'something', 'somethingawesomeandcool', 'cool']));