How to write a function that recognises unbalanced brackets

Question

I am trying to write a function that checks if a syntax is correct or not. If it is correct it returns \'ok\' else it returns the index of the error. So far my code works if

Answer 1

You could take a an array for the index of each opening character and pop this if the related closing character is found.

If finished and the stack has no item, the syntax is ok, otherwise return an index or the index of the last pushed opening character.

Example:

code        comment
----------- ---------------------------
[][[[]][][]
[]          balanced
  [         error, this returns later 2
   [[]]     balanced
       []   balanced
         [] balanced
            finally a missing ]

function syntaxError(syntax) {
    const
        isOpening = c => /[<[{(]/.test(c),
        isClosing = c => /[>\]})]/.test(c),
        open = { '>': '<', ']': '[', '}': '{', ')': '(' };

    var stack = [],
        index,
        finished = Array
            .from(syntax)
            .every((c, i) => {
                var temp = stack[stack.length - 1];
                if (isOpening(c)) {
                    if (temp && temp.c === c) {
                        temp.indices.push(i);
                    } else {
                        stack.push({ c, indices: [i] });
                    }
                    return true;
                }
                if (isClosing(c)) {
                    if (temp && temp.c === open[c]) {
                        temp.indices.pop();
                        if (!temp.indices.length) stack.pop();
                    } else {
                       index = stack.length ? stack.pop().indices.pop() : i;
                       return false;
                    }
                }
                return true;
            });

    return finished && !stack.length
        ? 'ok'
        : index === undefined
            ? stack.pop().indices.pop()
            : index;
}

console.log(syntaxError('[][][[{}]]'));  // ok

console.log(syntaxError(')'));
//                       0

console.log(syntaxError('[][][[{<}]]'));
//                       01234567

console.log(syntaxError('[][[[]][][]'));
//                       012

console.log(syntaxError('[[[[[[[[[[[[[[]]]]]]]]<<<<<<<<<<<>>>>>>>>>>>]]]]]]'+'[[[[[[[[[[[[[[]]]]]]]<<<<<<<<<<<>>>>>>>>>>>]}]]]]' + '>'));