Argument of type 'string | number | string[] | undefined' is not assignable to parameter of type 'string' when converting JavaScript to TypeScript

I’m trying to covert the following JavaScript function to TypeScript and I’m getting the following error

$("#checkoutSubmit").click(function () {
    var departureDate = $("#bookingDepartureDateInput").val();
  localStorage.setItem("datevalue", departureDate);
  console.log(localStorage.getItem("datevalue"))
});

I’ve never used TypeScript and I seem to be struggling with converting this. Can I get some insight on how to rewrite this code in TypeScript? Thank you.

>Solution :

the JQuery val(); method can return a String, Number or Array<string> this causes an error because localStorage.setItem only accepts strings.

If you are sure that $("#bookingDepartureDateInput").val(); always returns a string you can use as string to tell typescript that it can assume it will be a string:

$("#checkoutSubmit").click(function () {
  const departureDate = $("#bookingDepartureDateInput").val() as string;
  localStorage.setItem("datevalue", departureDate);
  console.log(localStorage.getItem("datevalue"))
});

JQuery .val() docs.