Question

I have a weird issue with this code

Moonbeam.Input.KeyboardState = function Moonbeam_Input_KeyboardState() {
    this._keys = new Array(2);
    this._resetKeys(); 
    } 

    Moonbeam.Input.KeyboardState.prototype = {

    _resetKeys: function Moonbeam_Input_KeyboardState$_resetKeys() {
        this._keys.clear();
    },

    _SetKeys: function Moonbeam_Input_KeyboardState$_SetKeys(keysPressed) {
        this._resetKeys();
        this._keys = keysPressed;
    }
}

I call the _SetKeys function and pass in a value, on the line this._resetKeys(); KeysPressed contains the value, on the line this._keys = KeysPressed, after returning from the call to _resetKeys(), keysPressed contains no value.

this is not the behaviour I expect, but javascript is not my speciality.

Can anyone tell me is this something I am doing wrong?

Is this how javascript works – I dont see how you could do recursion if it is.

I have also tried adding the line var _keysPressed = keysPressed; before the call to this._resetkeys() in the _SetKeys function but that also loses its value.

How do I get my values to stay during a call to another function?

stu.

Answer 1

When you pass an array (or object parameter) to a function, it is not copied, the function receives a reference to that array. When you then do this._keys = keysPressed;, _keys contains that same reference. When you later do this._keys.clear();, you’re modifying that array.

I suspect what’s happening is that you’re calling _setKeys() with the same array as the previous call. So when it calls this._resetKeys(), it clears that array.

You either need to create new arrays as you need them, perhaps by copying them when receiving them as parameters or returning them as values.