t1.html
1.<html>
2.<head></head>
3.<script>
4.function showpage(){
5. alert(showModalDialog("t2.html"));
6.}
7.</script>
8.<body>
9.<button οnclick="showpage()">show page</button>
10.</body>
11.</html>
t2.html
1.<html>
2.<head></head>
3.<script>
4.function setval(){
5.returnValue="abc";
6.close();
7.}
8.</script>
9.<body>
10.<button οnclick="setval()">set value</button>
11.</body>
12.</html>