var date = new Date(parseInt(jsonDate.substr(6)));
The substr() function takes out the /Date( part, and the parseInt() function gets the integer and ignores the )/ at the end. The resulting number is passed into the Date constructor.
I have intentionally left out the radix (the 2nd argument to parseInt); see my comment below.
Also, I completely agree with Rory's comment: ISO-8601 dates are preferred over this old format - so this format generally shouldn't be used for new development.
For ISO-8601 formatted JSON dates, just pass the string into the Date constructor:
var date = new Date(jsonDate); //no ugly parsing needed; full timezone support
Best Solution
You can do it in the css
Freeze Header: 1. Define class .Freezing in Stylesheet:
2.Assign Datagrid Header's cssClass to Freezing