closing tags Maciej chelange

gistfile1.js

// char => char
function closingTag(char) {
    return {
        '(': ')',
        '{': '}',
        '[': ']'
    }[char];
}

// char => boolean
function isClosingTag(c) {
    return c === ')' || c === ']' || c === '}';
}

// array, string => array
function notMatchingTags(openTags, tag) {
    if (isClosingTag(tag)) {
        if (tag === closingTag(openTags[openTags.length - 1])) {
            openTags.pop();
        } else {
            openTags.push('X'); // special char no closing to match
        }
    } else {
        openTags.push(tag);
    }
    return openTags;
}

// str => boolean
function isValidParenthesis(str) {
    return str.split('').reduce(notMatchingTags, []).length === 0;
}

console.log(isValidParenthesis("{}"))   //true
console.log(isValidParenthesis("{]"))   //false
console.log(isValidParenthesis("{{}}")) //true