Is Balanced

is-balanced.js

function isBalanced(expr) {
  let stack = [];

  for (let i = 0, length = expr.length; i < length; i++) {
    if (expr[i] === '{') {
      stack.push(expr[i]);
    } else if (expr[i] === '}') {
      if (stack.length > 0) {
        stack.pop();
      } else {
        return false;
      }
    }
  }

  if (stack.pop()) return false;
  return true;
}

var expression = "{{}}{}{}"
var expressionFalse = "{}{{}";

isBalanced(expression); // true
isBalanced(expressionFalse); // false
isBalanced(""); // true