Help reproducing transliteration scheme from Reconstructionist siddur? about hebrew-transliteration HOT 1 CLOSED

const transliteration = transliterate("אֵל חַי וְקַיָּם תָּמִיד יִמְלֹךְ עָלֵינוּ לְעוֹלָם וָעֶד׃", { customSchema });
// El ḥay vekayam tamid yimloḥ aleynu leolam vaed.

transliteration.split(" ").map(w => {
  const twoAdjacentVowels = /([aeiou])([aeiou])/g;
  return w.replaceAll(twoAdjacentVowels, "$1'$2");
}).join(" ");

// "El ḥay vekayam tamid yimloḥ aleynu le'olam va'ed."

const str = `אֵל חַי וְקַיָּם תָּמִיד יִמְלֹךְ עָלֵינוּ לְעוֹלָם וָעֶד׃`;

transliterate(str, {
  ...customSchema
  ADDITIONAL_FEATURES: [
    // if you customize your customSchema like I did here
    // don't forget the features you already have, or they will get overwritten
    {
      HEBREW: /[עא]/,
      FEATURE: "cluster",
      TRANSLITERATION: (cluster, _, schema) => {
        const syllable = cluster.syllable;
        const onset = syllable.onset;
        const clusterText = cluster.text;

        // this would mean that the alef or ayin do not contain a vowel
        if (onset != "ע" && onset != "א") {
          return clusterText;
        }

        // this would mean that there is no vowel preceding the alef or ayin, thus no need to add an apostrophe
        const prevSyllable = syllable.prev?.value;
        if (!prevSyllable) {
          return clusterText;
        }

        const key = onset === "ע" ? "AYIN" : "ALEF";

        return clusterText.replace(onset, "'" + schema[key]);
      }
    }
  ]
});

// el ḥay vekayam tamid yimloḥ alenu le'olam va'ed