How to set the value of MaskedEditExtender textbox to new value?

See more:

Javascript

Ajax

.NET4

My Requirement:

1. When user type in SSN text box it should look like this : 111-11-1111 - Which I have achieved.

2. On Textbox blur event I want that text to be converted to "***-**-1111, when I am assigning a new value to it,I am getting undefined value in it.

I will really appreciate if anybody will help me achieve this. The JavaScript code I have written :

var ssnValue = document.getElementById(<%=txtSSN.ClientID%>).value;

var lastfour = ssnValue.substring(7, 11);

1. var uSsn = "*****" + lastfour; Or
2. var uSsn = "***-**-" + lastfour;

Things Tried :
1. ssnValue.value = uSsn ;
2. ssnValue = uSsn .value;
3. ssnValue.value = uSsn .value;
4. ssnValue = uSsn ;