Javascript element is null [duplicate]

Question

I am a begginer at javascrit, and im trying to get a form result globaly

the radio button

<input type='radio' name='supporter' id='supporter' value='yes'>

and the javascript on the nother page

<script type="text/javascript">
function show(){
    var supporter = document.getElementById('supporter');
    if (supporter.value == "yes") {
        alert("it works")
    }
}

show();
</script>

and i keep getting an error, this: supporter is null

can please someone tell me what im missing?

Answer 1

It will depend on when the script is executed. Javascript is executed by the browser as it is encountered, which means that if your snippet of code exists in the page before the HTML element, then at that point in time, the HTML element does not yet exist.

One solution would be to put the Javascript at the very end of the page, or move that code into the document.onload handler.

document.onload = function () {
    show();
};