Question

I’m creating a small game and I have a peace of code that collects the pressed keys during an interval of time.

var pressedKeys = [];

setTimeout(function() {
     for(var i = 0; i < pressedKeys.length; i++)
     alert("Time is up you have inputed " + pressedKeys[i] + " length " + pressedKeys.length);
}, 3000);

$(document).keydown(function(evt) {
    var key = evt.keyCode;
if (pressedKeys.length < 1) {
    pressedKeys[0] = key;
} else {
    pressedKeys[pressedKeys.length + 1] = key;
}
});

I’m new to javascript and I can’t understand why I have unidentified values in the array. The funny thing to me is if I do the loop with a foreach I do not get the unidentified values.

Can some one please explain this to me. I would be very thankful.

Answer 1

This…

pressedKeys[pressedKeys.length + 1] = key;

should be this…

pressedKeys[pressedKeys.length] = key;

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Since Array indices are zero-based, the current last item in the Array will be its length - 1, which means the next item to fill will be the one at its .length.

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You can actually get rid of the if statement…

$(document).keydown(function(evt) {
    pressedKeys[pressedKeys.length] = evt.keyCode;
});

It starts off with a .length of 0, so the first entry will be at index 0, which makes the .length equal to 1, so the next entry will be at index 1, and so on…