Javascript implementation for Trie using RegEx

trie.js

// This code is translated to JS from Python in https://stackoverflow.com/a/42789508/1202830 on StackOverflow.
// Answered by Eric Duminil <https://stackoverflow.com/users/6419007/eric-duminil> on March 14, 2017
// Edited by Just a learner <https://stackoverflow.com/users/170931/just-a-learner> on April 29, 2019
// Translated to JS by @ptsgrn <https://www.github.com/ptsgrn>
// Released under CC BY-SA 4.0 <https://creativecommons.org/licenses/by-sa/4.0/>

class Trie {
  constructor() {
    this.data = {};
  }

  add(word) {
    let ref = this.data;
    for (const char of word) {
      ref[char] = char in ref ? ref[char] : {};
      ref = ref[char];
    }
    ref[""] = 1;
  }

  dump() {
    return this.data;
  }

  quote(char) {
    return /[\\^$.*+?()[\]{}|]/.test(char) ? `\\${char}` : char;
  }

  _pattern(pData) {
    const data = pData;
    if ("" in data && Object.keys(data).length === 1) {
      return "";
    }

    const alt = [];
    const cc = [];
    let q = 0;
    for (const char of Object.keys(data).sort()) {
      if (typeof data[char] === "object") {
        try {
          const recurse = this._pattern(data[char]);
          alt.push(`${this.quote(char)}${recurse}`);
        } catch (e) {
          cc.push(this.quote(char));
        }
      } else {
        q = 1;
      }
    }
    const cconly = alt.length === 0;

    if (cc.length > 0) {
      if (cc.length === 1) {
        alt.push(cc[0]);
      } else {
        alt.push(`[${cc.join("")}]`);
      }
    }

    if (alt.length === 1) {
      var result = alt[0];
    } else {
      result = `(?:${alt.join("|")})`;
    }

    if (q) {
      if (cconly) {
        result += "?";
      } else {
        result = `(?:${result})?`;
      }
    }
    return result;
  }

  pattern() {
    return this._pattern(this.dump());
  }
}

const trie = new Trie();
trie.add("foo");
trie.add("bar");
trie.add("baz");
trie.add("qux");
trie.add("quux");
trie.add("quuz");
trie.add("corge");
trie.add("grault");

console.log("trie.dump():", JSON.stringify(trie.dump(), null, 2));
const pattern = new RegExp(trie.pattern());
console.log("pattern:", pattern);
console.log("pattern.test('foo'):", pattern.test("foo"));
console.log("pattern.test('bar'):", pattern.test("bar"));
console.log("pattern.test('baz'):", pattern.test("baz"));
console.log("pattern.test('unknown'):", pattern.test("unknown"));