There are two mistakes here, You need to surround id with ” (Double Quotes) You should put script tag after the dom element is created, else it may execute before the actual dom is created. Even if you keep js code in a separate file, make sure you write it after your dom, just before the body tag ends. So your code should be … Read more
At the point you are calling your function, the rest of the page has not rendered and so the element is not in existence at that point. Try calling your function on window.onload maybe. Something like this:
It’s document.getElementById() and not document.getElementByID(). Check the casing for Id.
It can be caused by: Invalid HTML syntax (some tag is not closed or similar error) Duplicate IDs – there are two HTML DOM elements with the same ID Maybe element you are trying to get by ID is created dynamically (loaded by ajax or created by script)? Please, post your code.
I think the easiest approach would be to just check that el is not null before adding an event listener: