How do I get the TextBox Value since JavaScript? (Resolved)

Hey guys, i wanna get the TextBox Value since Js i tried it but no work:

var mystring= document.getElementById('MyIdTextBox').value;

and check with:

alert(mystring);

I specify in the construct2 the id as MyIdTextBox.

Please help

it's working for me...

ohh man soo cool, I can create external functions and then call with this, thank you.