Question

I have two text boxes t1 and t2 in an html page.

I’d like to copy t1 content to t2, using javascript on every keystroke done in t1.

Answer 1

Ol’ school, since you added the “beginner” tag:

<input type="text" id="t1" onkeyup="document.getElementById('t2').value = this.value" />
<input type="text" id="t2" />

A more robust solution also uses the change event (for those who paste via mouse right-click), and doesn’t inline the event handler logic:

<input type="text" id="t1" />
<input type="text" id="t2" />

<script>
var t1 = document.getElementById('t1');
t1.onkeyup = t1.onchange = function() {
    document.getElementById('t2').value = this.value;
};
</script>