random.js

/**
 * braces/brackets/parentheses validator
 */
function check(str) {
    const closers = {
        ')' : '(',
        '}' : '{',
        ']' : '['
    };
    const openers = {
        '(' : true,
        '{' : true,
        '[' : true
    };
    const all = [];
    
    for (let i = 0; i < str.length; i++) {
        let char  = str.charAt(i);
        
        if (closers[char]) {
            if (all.length === 0) return false;
            
            let opener = all[all.length - 1];
            
            if (closers[char] === opener) {
                all.pop();    
            }
        } else if (openers[char]) {
            all.push(char);
        }
    }
    
    
    // Is valid if no outstanding opener
    return all.length === 0;
}

// test cases
console.log(check(''));
console.log(check('{ s[ dfg]fdgdfg ( ) }'));
console.log(check('{ [ ( ] ) }'));
console.log(check('{ [ }'));
console.log(check('}'));