with | NN 2 IE 3 ECMA 1
The with statement adds an object to the scope of every statement nested within. This can shorten the code of some statement groups that rely on a particular object reference. Note that with constructions are generally very inefficient. You can achieve better performance by assigning the object reference to a local variable, and using that variable in your function.
Example
    with (document.forms[0]) {
        name1 = firstName.value;
        name2 = lastName.value;
        mail = eMail.value;
    }