Checking when capslock is turned on

I've written this JQuery program for checking whenever caps lock is turned on.

$("input[type='password']").keypress(function(e) {
    var kc = e.which; //get keycode
    var isUp = (kc >= 65 && kc = 97 && kc <= 122) ? true : false; // lowercase
    // event.shiftKey does not seem to be normalized by jQuery(?) for IE8-
    var isShift = ( e.shiftKey ) ? e.shiftKey : ( (kc == 16) ? true : false ); // shift is pressed

    // uppercase w/out shift or lowercase with shift == caps lock
    if ( (isUp && !isShift) || (isLow && isShift) ) {
        capLock(); // alerts "CAPSLOCK is ON"
    }

});
function capLock() {
 alert('CAPSLOCK is ON');
}

Turning my comment on your question into an answer:

On a Mac, when the Caps Lock key is engaged, the Shift key doesn't change the case to lower. So in the event that the Caps Lock key has already been engaged, before your page even loads, this code won't work as intended. I believe this jQuery plugin has already solved this problem - github.com/nosilleg/capslockstate-jquery-plugin

As for your code itself:

• I like that you've got named variables, that makes the final if statement super easy to read. You could name the event variable as such too, so it's clearer what e contains.

• You can refactor this var isUp = (kc >= 65 && kc

to:

var isUp = (kc >= 65 && kc <= 90) // uppercase

because (kc >= 65 && kc

to:

var isShift = ( e.shiftKey ) || (kc == 16);

The interesting thing about the statement above is that it takes advantage of a mechanism called short-circuit evaluation that boolean operators, like OR (||) and AND (&&), use.

Basically, in an OR statement, if the first expression evaluates to true, the second expression is never evaluated, because true || anything will always evaluate to true.

Similarly for an AND statement, if the first expression evaluates to false, the second expression is never evaluated, because false && anything will always evaluate to false.

StackExchange Code Review Q#93168, answer score: 7