Notice: In python, The null of node data judgement condition should be "\0" rather than "", " " or None.('\0' is treated simply as a character within a string.)

def decodeHuff(root, s):
    pointer = root
    decode_s = ""
    for c in s:
        if c=="1":
            pointer=pointer.right
        else:
            pointer = pointer.left
        if pointer.data!='\0':
            decode_s += pointer.data
            pointer = root
    print(decode_s)

simple python solution

def decodeHuff(root, s):
    node = root
    ans = ""
    for i in s:
        if node is None:
            return
        if i == "1":
            node = node.right
        elif i == "0":
            node = node.left
        if node.left is None and node.right is None:
            ans += node.data
            node = root
    print(ans)

JS version is not working. To get an idea of the structure of the 'input' variable I logged it to the console and passed all tests. The background process mentioned in the explanation that is supposed to encode the string is not present.

Heya there is a problem with the question when set to JS, simply console.logging the input will work and pass all tests

void decode(String s, Node root) {
    StringBuilder res = new StringBuilder("");
    Node move = root;
    for(int i = 0; i < s.length(); i++ ) {
        if(Objects.equals(s.charAt(i), '0')){

            move = move.left;

            if(move != null && move.left == null && move.right == null ) {
                res.append(move.data);
                move = root;
            }

        } else if(Objects.equals(s.charAt(i), '1')){

            move = move.right;

            if(move != null && move.left == null && move.right == null ) {
                res.append(move.data);
                move = root;
            }

        } 
    }

   System.out.println(res.toString());
}