Please explain about how to read a session variable in JavaScript which is defined externally.
Can we read this within the page?

Please explain about how to read a session variable in JavaScript which is defined externally.
Can we read this within the page?

use global variable in your ASPX file : var sessionValue = '<%= Session["YourKey"] %>'.
Now this global variable will be visible to the external JavaScript files that's included in the page.You can use "sessionValue" as you need.