Copying function from Script lab to excel js udf project gives errors 'CustomFunctions' is not defined

Question

I am new to office js. I created a udf project with shared runtime which contains clock, currenttime example function.

I added below the functions from script lab

/**
 * Returns the #NUM! error as part of a 2-dimensional array.
 * @customfunction
 * @param {number} first First parameter.
 * @param {number} second Second parameter.
 * @param {number} third Third parameter.
 * @returns {number[][]} Three results, as a 2-dimensional array.
 */
function returnInvalidNumberError(first, second, third) {
  // Use the `CustomFunctions.Error` object to retrieve an invalid number error.
  const error = new CustomFunctions.Error(
    CustomFunctions.ErrorCode.invalidNumber // Corresponds to the #NUM! error in the Excel UI.
  );

  // Enter logic that processes the first, second, and third input parameters.
  // Imagine that the second calculation results in an invalid number error.
  const firstResult = first;
  const secondResult = error;
  const thirdResult = third;

  // Return the results of the first and third parameter calculations
  // and a #NUM! error in place of the second result.
  return [[firstResult], [secondResult], [thirdResult]];
}

It gives 'CustomFunctions' is not defined. also 'returnInvalidNumberError' is declared but its value is never read.

Now this function works from script lab, so it should work from js project as well, but it doesnt. I am doing something wrong.

I tried adding package for customfunction but didnt work