Previous Page Button

There was a post that was closed about a year ago that showed the following:

Add the below to the visual editor for the pages you want the button to show:

<input type=”button” value=”Previous Page” onclick=”goBack()”>

<script>
function goBack() {
window.history.back()
}
</script>

My problem is that, if I copy and paste into the visual editor, I don’t get the button and the text that I pasted in appears on the actual page. If I paste it into the text editor, I get the button and it works. But, then if I use the visual editor, the button no longer works. I am doing something wrong.