how to change the input html dynamically code example

Example 1: how to change to input of a form dynamically

<input type="text" name="chance" value="50"
onchange="document.getElementById('payout').value='1/'+this.value+'x 98'">

Example 2: how to change to input of a form dynamically

<input type="text" name="chance" value="50"
    onkeyup="document.getElementById('payout').value='1/'+this.value+'x 98'">