I have a website( which im not owner of) which has a text box with Id = "idName". I have written a javascript function which has to fill the text box with my custom string :

function task() {
      //Below is my webpage which has a textbox with id = "idName"

      var popup = window.open("https://somewebsite.com");
      popup.onload = function(){
        document.getElementById("idName").value = "Hello World";
        popup.location.reload();
      }
      
  }

But the text box is not filled with "Hello World", it is empty. What mistake am i doing here ?