Parentheses matching in JavaScript

example.js

try {
  console.log(balanced('()'));
  console.log(balanced('(x()x)'));
  console.log(balanced('(this "))))")'));
  console.log(balanced('(multiple) (expressions) (in) (one) (string)'));
  console.log(balanced('(x()x'));
  console.log(balanced('{foo [bar]}'));
  console.log(balanced('(x([)]x'));
} catch (e) {
  console.log(e.message);
}

matching.js

// Copyright (C) 2024 Jakub T. Jankiewicz <https://jcubic.pl/me>
// Released under MIT license

class Stack {
    #data;
    constructor() {
        this.#data = [];
    }
    push(item) {
        this.#data.push(item);
    }
    len() {
        return this.#data.length;
    }
    top() {
        return this.#data[this.len() - 1];
    }
    pop() {
        return this.#data.pop();
    }
    is_empty() {
        return !this.#data.length;
    }
}

const tokens_re = /("[^"\\]*(?:\\[\S\s][^"\\]*)*"|[()[\]{}]|\n|\s+|[^\s()]+)/

function tokenize(string) {
    string = string.trim();
    if (!string.length) {
        return [];
    }
    return string.split(tokens_re).filter(token => token.trim());
}

function balanced(str) {
    // pairs of matching brackets
    const maching_pairs = {
        '[': ']',
        '(': ')',
        '{': '}'
    };
    const open_tokens = Object.keys(maching_pairs);
    const brackets = Object.values(maching_pairs).concat(open_tokens);
    // we filter out what is not a bracket
    // instead of tokenize you can use str.split('')
    const tokens = tokenize(str).filter(token => {
        return brackets.includes(token);
    });
    const stack = new Stack();
    for (const token of tokens) {
        if (open_tokens.includes(token)) {
            stack.push(token);
        } else if (!stack.is_empty()) {
             // there are brackets on the stack
            const last = stack.top();
            // the last opening character needs to match
            // the closing bracket we have
            const closing_token = maching_pairs[last];
            if (token === closing_token) {
                stack.pop();
            } else {
                // the character don't match
                throw new Error(`Syntax error: missing closing ${closing_token}`);
            }
        } else {
            // this case when we have closing token but no opening one,
            // becauase the stack is emtpy
            throw new Error(`Syntax error: not matched closing ${token}`);
        }
    }
    return stack.is_empty();
}