Upper case


please help me how to work the upper case
my code is
var user = prompt("What is your name please?").toUpperCase();
whats wrong with that??
the box says TypeError: Cannot read property 'toUpperCase' of null
please help me
this is the link


Either you have disabled popup in your Browser
or you will have to do a refresh Browser

++++ reset of session *****************
under certain circumstances you can shoot your Browser in an
inconsistent state.

Therefor it is of an advantage to know that you have 2 reset facilities:

One is the use of the F5-key which does a refresh Browser


Two, select&copy your code
Then use the Reset Code button of the course-window,
then paste your code back in.

General Notes:
Always refresh the browser after making corrections:
CTRL f5 ( if on Windows or Linux)
CMD r ( if on a MAC).
CTRL 0 to reset browser zoom