Failed to create Library. Unable to parse ****.js. Check for syntax errors and try creating again

Summary:

I am trying to upload a JavaScript file to OIC Library, but it prompts: "Failed to create Library. Unable to parse checkBizUnit.js. Check for syntax errors and try creating again."

I verified the functionality of the js file with node.js, it worked well. But don't know why OIC refuse the upload due to syntax issue. Even though I simplify the function to just a few lines, the issue persists.

//------ checkBizUnit.js ------

function only_cn_supplier_flag () {

  let onlyCnBu = true;

  return onlyCnBu;

}

//------------------------------

Is there any way to figure out which line causes the syntax error for OIC?