@technobuddha/library/src/syllables.ts

A large library of useful functions

import { splitWords } from './split-words.ts';
import { toASCII } from './to-ascii.ts';
import { empty } from './unicode.ts';

/**
 * Approximate the number of syllables in a string
 * @param input - The string
 * @returns the number of syllables
 * @example
 * ```typescript
 * syllables('hello'); // 2
 * syllables('syllable'); // 3
 * ```
 * @group String
 * @category Analysis
 */
export function syllables(input: string): number {
  return splitWords(toASCII(input.toLocaleLowerCase())).reduce((c, w) => {
    let count = c;
    let word = w;

    if (word.length <= 3) {
      count++;
    } else {
      // cspell:ignore laeiouy
      word = word.replace(/(?:[^laeiouy]es|ed|[^laeiouy]e)$/u, empty).replace(/^y/u, empty);

      const match = word.match(/[aeiouy]{1,2}/gu);
      count += match === null ? 0 : match.length;
    }

    return count;
  }, 0);
}