Null Variable in Javascript Code -

it keeps saying variable null though assigned button in html. doesn't allow button press work. variable "clickme"

var yourname;   //global variable accessible functions  function showanothermessage() {     alert("hi " + yourname + ".\nthis alert message no longer defined\nin html in javascript file"); }  function init() {     yourname = prompt("hi. enter name.\nwhen browser window first loaded\nthe function containing prompt window called.", "your name");     var clickme = document.getelementbyid("buttonclick");   clickme.onclick = showanothermessage;     }  window.onload = init(); 

avoid window.onload because it's fired late in page lifecycle - it's fired after everything loaded, including images - can several seconds after page has loaded.

instead, use dom events api, , use domcontentloaded event:

window.addeventlistener('domcontentloaded', function(e) {      // page startup code goes here } ); 

another reason avoid window.onload = ... overwrite previous event-handler onload event, whereas addeventlistener not remove previous event handler.