[neurostep]

function copy_value_to(input, inputs) {
    var value = input.value;
    for(var i=0; i<inputs.length; i++) {
        inputs[i].value = value;
    }
}

<form>
	<input type="text" onkeyup="copy_value_to(this, [document.getElementById('test')]);" value="" />
	<input id="test" type="text" value="" />
	<input type="text" value="" />
	<input type="text" value="" />
	<input type="text" value="" />
</form>