Balanced Parens

balanced_parens.js

var test = '{[()]}';

function balancedParens(str) {
  var parens = {
    '{': '}',
    '[': ']',
    '(': ')'
  }
  var stack = []
  for (var i = 0; i < str.length; i++) {

    // Check if i is an opener and push onto stack
    if (parens[str[i]]) 
    {
      stack.push(str[i]);
    } 

    /**
     * If it's a closing paren, pop off the last known opener,
     * check to ensure the stack is not empty, then ensure it
     * corresponds to the correct closer.
     */
    
    else 
    {
      var opener = stack.pop();
      if (!opener) return false;
      if (parens[opener] != str[i]) return false;
    }
  }
  return stack.length === 0;
}

console.log(balancedParens(test))