awesome-string/src/count/count_substrings.js

The ultimate JavaScript string library

import coerceToString from 'helper/string/coerce_to_string';

/**
 * Counts the number of `substring` appearances in `subject`.
 *
 * @function countSubstrings
 * @static
 * @since 1.0.0
 * @memberOf Count
 * @param  {string} [subject=''] The string where to count.
 * @param  {string} substring    The substring to be counted.
 * @return {number}              Returns the number of `substring` appearances.
 * @example
 * as.countSubstrings('bad boys, bad boys whatcha gonna do?', 'boys');
 * // => 2
 *
 * as.countSubstrings('every dog has its day', 'cat');
 * // => 0
 */
export default function countSubstrings(subject, substring) {
  const subjectString = coerceToString(subject);
  const substringString = coerceToString(substring);
  const substringLength = substringString.length;
  let count = 0;
  let matchIndex = 0;
  if (subjectString === '' || substringString === '') {
    return count;
  }
  do {
    matchIndex = subjectString.indexOf(substringString, matchIndex);
    if (matchIndex !== -1) {
      count++;
      matchIndex += substringLength;
    }
  } while (matchIndex !== -1);
  return count;
}