Got error on passing method as parameter on another method inside class

class Parser {
 private tokens: Array<ITokenized>
 private token_index: number;
 private current_token: ITokenized | undefined;

 constructor(tokens: Array<ITokenized>) {
  // console.log(tokens);
  this.tokens = tokens
  this.token_index = -1;
  this.current_token = undefined
  this.next()
 }

 next() {
  this.token_index += 1;
  if (this.token_index < this.tokens.length) {
   this.current_token = this.tokens[this.token_index]
  }
  return this.current_token
 }

 public parse(): any {
  let result = this.expression();
  return result;
 }

 private factor() {
  let token = this.current_token
  if ([TOK_INT, TOK_FLOAT].includes(token?.dataType)) {
   this.next();
   return new NumberNode(token?.value).represent();
  }
 }

 private term() {
  return this.binaryOperation(this.factor, [TOK_MULTI, TOK_DIVI])
 }

 private expression() {
  return this.binaryOperation(this.term, [TOK_PLUS, TOK_MINUS])
 }

 public binaryOperation(func: Function, operator: Array<string>) {
  let leftNode, operationToken, rightNode;
  leftNode = func()
  while (operator.includes(this.current_token?.dataType)) {
   operationToken = this.current_token;
   this.next();
   rightNode = func()
   leftNode = new BinaryOperator(leftNode, operationToken?.dataType, rightNode).represent();
  }

  return leftNode;
 }
}


export default Parser;