check correct order of the brackets in expression

index.js

/**
 * @param {string} str testable string
 *
 * @return {boolean}
 */
function verify(str) {
  if (typeof str !== 'string') return false;

  var pairs = {
    '(' : ')',
    '{' : '}',
    '<' : '>',
    '[' : ']',
  };
  var reversPairs = {
    ')' : '(',
    '}' : '{',
    '>' : '<',
    ']' : '[',
  };

  var stack = [];

  for (var i = 0, ilen = str.length; i < ilen; i++) {
    var char = str.charAt(i);
    if (pairs[char] !== undefined) {
      stack.push(char);
    } else if (reversPairs[char] !== undefined) {
      var last = stack.pop();

      if (last !== reversPairs[char]) return false;
    }
  }

  return !stack.length;
} // end verify()

console.log('verify("")', verify(""));
console.log('verify("before ( middle []) after ")', verify("before ( middle []) after "));
console.log('verify(") (")', verify(") ("));
console.log('verify("} {")', verify("} {"));
console.log('verify("<(   >)")', verify("<(   >)"));
console.log('verify("(  [  <>  ()  ]  <>  )")', verify("(  [  <>  ()  ]  <>  )"));
console.log('verify("   (      [)")', verify("   (      [)"));

console.log('verify("---(++++)----")', verify("---(++++)----"));
console.log('verify("")', verify(""));
console.log('verify("before ( middle []) after ")', verify("before ( middle []) after "));
console.log('verify(") (")', verify(") ("));
console.log('verify("} {")', verify("} {"));
console.log('verify("<(   >)")', verify("<(   >)"));
console.log('verify("(  [  <>  ()  ]  <>  )")', verify("(  [  <>  ()  ]  <>  )"));
console.log('verify("   (      [)")', verify("   (      [)"));