Javascript alert coming up when not expected

Question

I am trying to ensure that all fields of a form are not empty. When there are empty fields this alert comes up as expected, however when all fields are full the alert still comes up. Am I missing something?

var sn = document.myForm.address.length;
var sna = document.myForm.street.length;
var su = document.myForm.city.length;
var st = document.myForm.state.length;
var usn = document.myForm.username.length;

if (sn || sna || su || st || usn == null) {
    alert("All fields are required. Please ensure you leave no fields blank."); 
    return false;   
} else {

}

Answer 1

Since you initialized all your variables, your if statement is evaluating true like this:

if (true || true || true || true || true || false)

Only one true makes the entire if condition above evaluate to true because all the || operators are OR operators.

Consider further, if you simply declare but do not initialize a variable for example var sn; //declared var sn; //declared as opposed to var sn = document.myForm.address.length; //initialized var sn = document.myForm.address.length; //initialized then its condition evaluates to false because if(sn) is declared but not initialized = false`.

Moreover, to check the value inside each variable rather than whether or not they are initialized, you must do this:

if (sn == null || sna == null || su == null || st == null || usn == null)

or possibly since you're assigned a length you want this

if (sn > 0 || sna > 0 || su > 0 etc...