Keyboard.Extra's internal message type.

The subscriptions needed for the "Msg and Update" way.

Use this (or updateWithKeyChange) to have the list of keys update.

If you need to know exactly what changed just now, have a look at updateWithKeyChange.

This alternate update function answers the question: "Did the pressed down keys in fact change just now?"

You might be wondering why this is a Maybe KeyChange – it's because keydown events happen many times per second when you hold down a key. Thus, not all incoming messages actually cause a change in the model.

Note This is provided for convenience, and may not perform well in real programs. If you are experiencing slowness or jittering when using updateWithKeyChange, see if the regular update makes it go away.

The second value updateWithKeyChange may return, representing the actual change that happened during the update.

Record type used for arrows and wasd. Both x and y can range from -1 to 1, and are 0 if no keys are pressed.

Gives the arrow keys' pressed down state as follows:

arrows []                                   --> { x = 0, y = 0 }


arrows [ ArrowLeft ]                        --> { x = -1, y = 0 }


arrows [ ArrowUp, ArrowRight ]              --> { x = 1, y = 1 }


arrows [ ArrowDown, ArrowLeft, ArrowRight ] --> { x = 0, y = -1 }

Similar to arrows, gives the W, A, S and D keys' pressed down state.

wasd []                       --> { x = 0, y = 0 }


wasd [ CharA ]                --> { x = -1, y = 0 }


wasd [ CharW, CharD ]         --> { x = 1, y = 1 }


wasd [ CharA, CharS, CharD ]  --> { x = 0, y = -1 }

Type representation of the arrows.

Gives the arrow keys' pressed down state as follows:

arrowsDirection []                      --> NoDirection


arrowsDirection [ ArrowLeft ]           --> West


arrowsDirection [ ArrowUp, ArrowRight ] --> NorthEast


arrowsDirection [ ArrowDown, ArrowLeft, ArrowRight ] --> South
-- (left and right cancel out)

Similar to arrows, gives the W, A, S and D keys' pressed down state.

wasdDirection []                      --> NoDirection


wasdDirection [ CharA ]               --> West


wasdDirection [ CharW, CharD ]        --> NorthEast


wasdDirection [ CharA, CharS, CharD ] --> South

Subscription for key down events.

Note When the user presses and holds a key, there may or may not be many of these messages before the corresponding key up message.

Subscription for key up events.

A Json.Decoder for grabbing event.keyCode and turning it into a Key

import Json.Decode as Json


onKey : (Key -> msg) -> Attribute msg
onKey tagger =
    on "keydown" (Json.map tagger targetKey)

Convert a key code into a Key.

fromCode 13  --> Enter

Convert a Key into a key code.

toCode Enter  --> 13

These are all the keys that have names in Keyboard.Extra.