Create a function that checks if parentheses and brackets are correctly balanced in a string

isBalance.js

var isBalance = function(str) {
  if(str.length < 1) return false;
  let pairs = {
    '(': ')',
    '{': '}',
    '[': ']'
  };
  let openers = []; // replace [] with: new Stack
  
  for (let index in str) {
    let char = str[index];
    if (pairs[char]) {
      openers.push(char);
    } else if (Object.values(pairs).includes(char)) {
      let popped = openers.pop();
      if(pairs[popped] != char) {
        return false;
      }
    }
  }
  return openers.length == 0;
}

//test cases
isBalance('({}())') // true
isBalance('({)}') // false
isBalance('(this{works})') // true
isBalance('[[()') // false

Good job! Since I'm a pain in the ass here are some more tips:

• print out your tests or use console.assert(isBalance("something") === true) for easier debugging. the console assert will raise an error if it does not pass.
• you are using let but I believe all of these variables could be const which is preferred because then you know if it is expected to change or will change.
• the input string might be null not just empty. So your initial guard is probably simplified as just simply if (!str) return false;
• I'm not crazy about the name popped. its not bad but I would prefer something like opener, but no biggie.

I think calling it openers is better than calling that variable stack although each has its own advantages.

One recommendation for more readable code might be to have allOpeners and allClosers arrays, that way we can write it like this

if (allOpeners.includes(char)) {
  openers.push(char)
} else if (allClosers.includes(char)) {
  const lastOpener = openers.pop();
  if (getMatchingOpener(lastOpener) !== char) return false;
}

Anyway, good job!