01219245/javascript1/tutorial3/2

Your current JavaScript program in the script block probably look like this:

var numSticks = 21;

function pickSticks() {
    var num = parseInt( $( "#pickNum" ).val() );
    numSticks -= num;
    $( "#numSticks" ).text( numSticks );
}

$(function(){
    $("#pickButton").click(pickSticks);
});

Valid number of sticks

Let's add the code that check that the number of sticks the player want to take is valid, i.e., it is between 1 to 3 and is no larger than the current number of sticks. Let's assume that the input is an integer for now (i.e., that the user won't enter 1.5). If the amount is invalid, let's throw an alert for now.

function pickSticks() {
    var num = parseInt( $( "#pickNum" ).val() );
    if ( ( num >= 1 ) && ( num <= 3 ) && ( num <= numSticks ) ) {
        numSticks -= num;
        $( "#numSticks" ).text( numSticks );
    } else {
        alert( "Invalid amount.  Please try again" );
    }
}