Custom Iterators

iterators.arrays.js

/** Creates an array that, when iterated, only returns ruthy items
 * @param  {array} iterable
 *
 * @example const mixedBag = new TruthyArray(1, 0, 'foo', '', true, false, undefined, null, 'three'])
 * for (item of mixedBag) {
 *   console.log(item);
 * }
 * 
 */
class TruthyArray extends Array {
    constructor(value) {
        super(...value);  
        this.value = [...value];
    }
    get [Symbol.species]() {
      return Array;
    }
    *[Symbol.iterator]() {
      let itemIndex = -1;
          while (itemIndex < this.value.length ) {
              if (this.value[++itemIndex]) {
                  yield this.value[itemIndex];
              }
          }
      }
  }

iterators.strings.js

/** returns a string whose iterator will iterate by whole words
 * @param  {string} text
 */
function WordString(text) {
    const string = new String(text); // make explicit object
    const words = string.split(' '); // split by spaces
    let wordIndex = 0;

    string[Symbol.iterator] = function* stringIterator() {
      while (wordIndex < words.length) {
       yield words[wordIndex++]
        .replace(new RegExp('[!.?]', 'g'),''); // remove any punctuation
      }
    }
  
    return string;
}

/** returns a string that can be iterated on by sentences
 * @param  {string} text
 *
 * @example const sentences = 'This is a sentence. Isn't this one? ¿Y también esta?'
 * for (sentence of sentences) {
 *  console.log(sentence);
 * }
 */
function SentenceString(text) {
    const string = new String(text);
    const sentences = string.split(new RegExp('[!.?]', 'g')); // capture by end punctuation
    let sentenceIndex = 0;

    string[Symbol.iterator] = function* SentenceIterator() {
        while (sentenceIndex < sentences.length) {
            yield sentences[sentenceIndex++]
                .replace(new RegExp('[¿¡]', 'g'),'')
                .trim(); // remove beginning punctuation and trim whitespace
        }
    }

    return string;
}