Input Helper Class

readme.md

This was written for a Stack Overflow answer

input.js

function Input(el){
    var parent = el,
        map = {},
        intervals = {};

    function ev_kdown(ev)
    {
        map[ev.key] = true;
        ev.preventDefault();
        return;
    }

    function ev_kup(ev)
    {
        map[ev.key] = false;
        ev.preventDefault();
        return;
    }

    function key_down(key)
    {
        return map[key];
    }

    function keys_down_array(array)
    {
        return typeof array.find( key => !key_down(key) ) === "undefined";
    }

    function keys_down_arguments(...args)
    {
        return keys_down_array(args);
    }

    function clear()
    {
        map = {};
    }

    function watch_loop(keylist, callback)
    {
        return function(){
            if(keys_down_array(keylist))
                callback();
        }
    }

    function watch(name, callback, ...keylist)
    {
        intervals[name] = setInterval(watch_loop(keylist, callback), 1000/24);
    }

    function unwatch(name)
    {
        clearInterval(intervals[name]);
        delete intervals[name];
    }

    function detach()
    {
        parent.removeEventListener("keydown", ev_kdown);
        parent.removeEventListener("keyup", ev_kup);
    }

    function attach()
    {
        parent.addEventListener("keydown", ev_kdown);
        parent.addEventListener("keyup", ev_kup);
    }

    function Input()
    {
        attach();

        return {
            key_down:  key_down,
            keys_down: keys_down_arguments,
            watch:     watch,
            unwatch:   unwatch,
            clear:     clear,
            detach:    detach
        };
    }

    return Input();
}

interface-reference.md

Here is the interface reference:

Boolean  key_down (String key);
Returns `true` if `key` is down, false otherwise.

Boolean  keys_down (String key1, String key2, ...);
Returns `true` if all keys `key1 .. keyN` are down, false otherwise.

void     watch (String name, Function callback, String key1, String key2, ...);
Creates a "watchpoint" such that pressing all of `keyN` will trigger the callback

void     unwatch (String name);
Removes said watchpoint via its name

void     clear (void);
Wipes the "keys down" cache. Equivalent to `map = {}` above

void     detach (void);
Detaches the `ev_kdown` and `ev_kup` listeners from the parent element, making it possible to safely get rid of the instance