how to interchange the variables between jsp, html and javascript?

[qkl]

1. If I have a var defined in javascript, can I use get its value outside javascript fragment? I means, not only to print out.

2. Or if I set a page/session scope variable defined by <c:set var="myVar" .../>. Could I change it's value within the javascript function and keep the changed value outside?

3. How can I get the value of a 'select' of a form before submit it by not using javascript?

How can give a advice? Thanks

[acoder]

1. If I have a var defined in javascript, can I use get its value outside javascript fragment? I means, not only to print out.

Yes, but it'd have to be within script tags or inline in a tag in an event handler, e.g. onclick.

2. Or if I set a page/session scope variable defined by <c:set var="myVar" .../>. Could I change it's value within the javascript function and keep the changed value outside?

You can generate JavaScript code using JSP, with a variable set to the session variable which could then be modified. However, this would have no effect on the server. To change server-side variables using JavaScript, you can use Ajax (JSP to change the variable values).

3. How can I get the value of a 'select' of a form before submit it by not using javascript?

Not possible without JavaScript.