How do you assign a JS variable to a Java variable in a JSP, or assign a Java variable to a JS variable?

In JSP often encounter the JS variable assigned to the Java variable, or the Java variable assigned to the JS variable case, here the general processing method summarized as follows:

Java variables passed to JS Good, var a= "<%=javaParam%>"; note to add the quotation marks "";

JS variable to java slightly more complex point, usually in the form with a
Hidden form elements, and then assigns the value of the JS variable to it in the script:

var jsparamvalue= ' aaaa ';
Form1.jsparam.value=jsparamvalue;

Then you can Request.getprameter ("Jsprama") to get the JS variable value.
You cannot assign a value to a Java variable on a page by taking a JS variable;
Instead, you can assign a Java variable to a JS variable with var jsparam = "<%=javaParam%>".