Reflect

<SCRIPT>

function echo(form, currentField) {
     if (currentField == "first")
          form.second.value = form.first.value;
     else
          form.first.value = form.second.value;
}

</SCRIPT>

<FORM>
     <INPUT TYPE="text" NAME="first" onChange="echo(this.form, this.name);">
     <INPUT TYPE="text" NAME="second" onChange="echo(this.form, this.name);">
</FORM>

This example illustrates an important point.

echo(this.form, this.name) passes 2 parameters:

this.form -- because we want to pass all the form's information to the function
this.name -- to tell the function what particular form element made the call