Question

I’m a newbie to scripting. I want to update HTML content with JavaScript, but as you can see
the web page keeps refreshing.

How can I prevent the page from refreshing?

Javascript:

function showResult(form) {
var coba=form.willbeshown.value;
var coba2=coba+2;
document.getElementById("showresulthere").innerHTML=coba2;
}

HTML

<form>
<input type="text" name="willbeshown" value="">
<button onclick="showResult(this.form)">Ganti1</button>
</form>
<p id="showresulthere">Result will be shown here</p>
</body>

Answer 1

Don’t use a form at all. You are not submitting any form data to a server. To process data in the browser, you don’t need a form. Using a form just complicates things (though such issues could be fixed by using type=button in the button element, to prevent it from acting as a submit button).

<input type="text" id="willbeshown" value="">
<button onclick=
  "showResult(document.getElementById('willbeshown'))">Ganti1</button>
<p id="showresulthere">Result will be shown here</p>
<script>
function showResult(elem) {
  document.getElementById("showresulthere").innerHTML = Number(elem.value) + 2;
}
</script>

I have used conversion to numeric, Number(), as I suppose you want to add 2 to the field value numerically, e.g. 42 + 2 making 44 and not as a string, 42 + 2 making 422 (which is what happens by default if you just use an input element’s value and add something to it.