Browser Keymap

A small library for doing sane key binding in the browser. It defines two things:

A string notation for key events

browserkeymap keys are represented by strings like "Shift-Space", "Ctrl-Alt-Delete", or "'x'". The rules are:

• keypress events are represented as the character that was typed between single quotes. They do not support modifiers because browsers do not attach modifier information to keypress events.

• keydown events are represented as zero or more modifiers (Shift-, Cmd-, Alt-, Ctrl-, in that order) followed by a key name.

• A key name is a capital letter for a letter key, F plus a number for a function key, the symbol typed by the key when shift isn't held down (one of [\]`'*,-./;=), or one of the names Alt, Backspace, CapsLock, Ctrl, Delete, Down, End, Enter, Esc, Home, Insert, Left, Mod, PageDown, PageUp, Pause, PrintScrn, Right, Shift, Space, Tab, or Up.

You can get a key name from an event by calling Keymap.keyName(event).

You can normalize a key name string (fixing the order of the modifiers, and replacing alternative modifier names with their standard name) by calling Keymap.normalizeKeyName(string). This function maps the modifier Mod- to Cmd- on Mac platforms and to Ctrl- on non-Mac platforms. It also accepts a- for Alt-, c- or Control- for Ctrl-, m- or Meta- for Cmd-, and s- for Shift-.

You can use Keymap.isModifierKey(string) to find out whether the given key name refers to a modifier key.

An object type for keymaps

The Keymap constructor itself, which is the thing the library exports, can be used to build keymaps.

var myMap = new Keymap({
  "Ctrl-Q": handleQuit,
  "Shift-Space": autocomplete
})

A keymap associates keys with values. You can call its lookup method to look up a key:

myMap.lookup("Ctrl-Q") // → handleQuit
myMap.lookup("Alt-F4") // → undefined

You can add and remove bindings on an existing keymap.

myMap.addBinding("Alt-F4", handleQuit)
myMap.addBindings({"Enter": something, "Esc": something})
myMap.removeBinding("Shift-Space")

So far, this doesn't do anything that a JavaScript object couldn't do. The constructor accepts a second argument, which is an options object. These options are supported:

• multi: Boolean, defaults to true. Toggles support multi-stroke key bindings. Binding names may be space-separated strings containing multiple key names. The keymap will track which prefixes are part of a multi-stroke binding, and when such a prefix is looked up, it will return "...", to indicate to client code that it should buffer the key name, and, on the next non-modifier key event, try looking up that key name suffixed by the next key name (separated by a space).

• call: Function, defaults to null. When given, it makes this keymap a programmatic keymap, meaning the bindings are ignored and the function that is the value of the call option will be called, with the key name, when a key is looked up, and its return value returned.

License

This module is released under an MIT license.