validParentheses.js

/**
 * @param {string} s
 * @return {boolean}
 */

const reference = {
  '(': ')',
  '{': '}',
  '[': ']',
};

function isValid(string) {
  const stack = [];
  for (let i = 0; i < string.length; i++) {
    let target = string[i];
    if (reference[target]) {
      stack.push(reference[target]);
    } else {
      if (target != stack.pop()) {
        return false;
      }
    }
  }
  return stack.length == 0;
}