JSFiddle - React, Tailwind, and code Playground
HTML
<script>
function multiplicar(A,B)
{
var ASu=document.getElementById(A).value;
var BSu=document.getElementById(B).value;
C=ASu*BSu;
document.getElementById('Total').value=C;
}
</script>
<input type="text" id="texto1" onkeyup="multiplicar('texto1','texto2')" /><br />
<input type="text" id="texto2" onkeyup="multiplicar('texto1','texto2')" /><br />
<br />
Total <input type="text" id="Total" />