a.html
<script> function openOther(v){ var w = showModalDialog("b.html"); v.val.value=w; }</script>
<form> <input name="val"> <input type="button" οnclick="openOther(this.form);" value="click"></form>
<script> function sopen(vv){ var w = showModalDialog("b.html"); w = w + ""; if( w != "undefined" ){ vv.v.value = w; } }</script>
<form> <input name="v"> <input type="button" οnclick="sopen(this.form);" value="open"></form>
b.html
<script> function returnText(v){ window.returnValue = v.val.value; window.close(); }</script>
<form> <input name="val"> <input type="button" οnclick="returnText(this.form);" value="return"></form>
