Braces Validator

braces-validator.js

function validateBraces(braces) {
  const opening = ['(', '{', '['];
  const closing = [')', '}', ']'];
  if (closing.indexOf(braces[0]) !== -1 || opening.indexOf(braces[braces.length - 1]) !== -1) {
    // return if first bracket is closing or last is opening
    return false;
  }
  if (braces.length === 2) {
    // return if length is 2 and first and last don't match
    if ((braces[0] === opening[0] && braces[1] === closing[0]) ||
        (braces[0] === opening[1] && braces[1] === closing[1]) ||
        (braces[0] === opening[2] && braces[1] === closing[2])) { return true; }
  }
  // other cases
  while (braces.length > 0 && braces.length % 2 === 0) {
    const selectedBrace = braces[0];
    const selectedPairIndex = opening.indexOf(braces[0]);
    const closingIndexInInput = braces.indexOf(closing[selectedPairIndex]);
    /*
    *  handle symmetry
    */
    const left = braces.substring(0, braces.length / 2).split('');
    const right = braces.substring(braces.length / 2, braces.length).split('').reverse();
    let sym = 0;
    if (left.length === right.length) {
      loop:
      for (let j = 0, jMax = left.length; j < jMax; j++) {
        if (opening.indexOf(left[j]) === closing.indexOf(right[j])) { sym++; }
        else { break loop; }
      }
      if (sym === left.length) { return true; }
    }
    /*
    *  handle everything else
    */
    if (closingIndexInInput === -1 ||
        (selectedPairIndex > 0 && (closingIndexInInput - 1) % 2 !== 0)) {
      return false;
    } else {
      braces = braces.slice(1);
      braces = (closingIndexInInput < braces.length - 1) ? braces.substring(0, closingIndexInInput - 1) + braces.slice(closingIndexInInput) : braces.substring(0, closingIndexInInput);
      if (braces.length % 2 !== 0) { braces = braces.substring(0, braces.length - 1); }
    }
  }
  return (braces.length % 2 !== 0) ? false : true;
}

validateBraces('(){}[]') // true
validateBraces('(}') // false
validateBraces('[(])') // false
validateBraces('([{}])') // true

BracesValidator.markdown

Braces Validator

Accepts nonempty string consisting on of opening and closing braces: '(', ')', '[', ']', '{', '}'. Returns true if sequence is valid, false is sequence is not valid.

A script by V.

License.