cannot read property of undefined (reading 'ajax')

I can't access webmethod within javascript. It gives the error in the title. Why might it be caused?

Js :

    function funcGoster() {
          $.ajax({
              type: "POST",
              url: "/WebService1.asmx/HelloWorld",
              data: "{}",
              contentType: "application/json; charset=utf-8",
              dataType: "json",
              success: function (msg) {
                //  document.getElementById('text').innerHTML = 
              },
              error: function (e) {
                  alert("başarısız" + e);

              }
          });
      }
</script>

WebMethod :

public class WebService1 : System.Web.Services.WebService
{

    [WebMethod]
    public static string HelloWorld()
    {
        return "Hello World";
    }
}

Via Active questions tagged javascript - Stack Overflow https://ift.tt/2FdjaAW