[Javascript] 95% speed, 100% memory - w/ comments
\nvar isSymmetric = function(root) {\n    if (root == null) return true;\n    \n    return symmetryChecker(root.left, root.right);\n};\n\nfunction symmetryCheck
```\nvar isSymmetric = function(root) {\n    if (root == null) return true;\n    \n    return symmetryChecker(root.left, root.right);\n};\n\nfunction symmetryChecker(left, right) {\n    if (left == null && right == null) return true; // If both sub trees are empty\n    if (left == null || right == null) return false; // If only one of the sub trees are empty\n    if (left.val !== right.val) return false; // If the values dont match up\n    \n\t// Check both subtrees but travelled in a mirrored/symmetric fashion\n\t// (one goes left, other goes right)  and make sure they\'re both symmetric\n    return symmetryChecker(left.left, right.right) &&\n    symmetryChecker(left.right, right.left);\n}\n```
['JavaScript']