How to use the antlr4ts.ParserRuleContext function in antlr4ts

function createSourceTree(
  antlrNode: antlr.ParserRuleContext | TerminalNode,
  fullCode: string,
  codePosition: { charIndex: number } = {
    charIndex: 0
  }
): Node[] {
  if (antlrNode instanceof antlr.ParserRuleContext) {
    let tree = new Tree(antlrNode.constructor.name);
    if (antlrNode.start.startIndex > codePosition.charIndex) {
      tree.children.push(
        new Space(
          fullCode.substring(codePosition.charIndex, antlrNode.start.startIndex)
        )
      );
      codePosition.charIndex = antlrNode.start.startIndex;
    }
    for (let i = 0; i < antlrNode.childCount; i++) {
      let child = antlrNode.getChild(i);
      if (
        child instanceof antlr.ParserRuleContext ||
        child instanceof TerminalNode
      ) {
        tree.children.push(...createSourceTree(child, fullCode, codePosition));

}
): Node[] {
  if (antlrNode instanceof antlr.ParserRuleContext) {
    let tree = new Tree(antlrNode.constructor.name);
    if (antlrNode.start.startIndex > codePosition.charIndex) {
      tree.children.push(
        new Space(
          fullCode.substring(codePosition.charIndex, antlrNode.start.startIndex)
        )
      );
      codePosition.charIndex = antlrNode.start.startIndex;
    }
    for (let i = 0; i < antlrNode.childCount; i++) {
      let child = antlrNode.getChild(i);
      if (
        child instanceof antlr.ParserRuleContext ||
        child instanceof TerminalNode
      ) {
        tree.children.push(...createSourceTree(child, fullCode, codePosition));
      } else {
        throw new Error("Unexpected child: " + child);
      }
    }
    if (antlrNode.stop!.stopIndex > codePosition.charIndex) {
      tree.children.push(
        new Space(
          fullCode.substring(
            codePosition.charIndex,
            antlrNode.stop!.stopIndex + 1
          )
        )
      );