keymage.js

Keymage is a small (1.6kb after Closure Compiler and gzip) library for handling key bindings in JavaScript. It supports nested application scopes, has a simple DSL for defining keys and can handle key chords.

- or check tests in browser

Features

• Simple language for defining bindings
• Key sequences (a-la Emacs chords)
• Nested scopes
• Default modifier (defmod key which is command on OS X and control elsewhere)
• Ability to prevent defaults for whole sequence

Usage

Include keymage.min.js in your page:

<script src="keymage.min.js"></script>

There are no dependencies. It is possible to use library as a simple JS module, as an AMD module or as CommonJS module.

It worth to note that Keymage is on cdnjs which enables you to use it without downloading.

Plus, of course, it's on NPM.

Defining shortcuts

Keymage exposes a single function, keymage:

// bind on 'a'
keymage('a', function() { alert("You pressed 'a'"); });

// returning false prevents default browser reaction (you can always use
// e.preventDefault(), of course)
keymage('ctrl-e', function() { return false; });

// binding on 'defmod' binds on Command key on OS X and on Control key in other
// systems
keymage('defmod-j', function() { alert("I am fired"); });

Handler function receives two arguments: the original event and the context so you can understand what and why was fired.

The context contains those properties:

• shortcut is a string you've originally provided for binding
• scope is a scope which is currently active
• definitionScope is a scope where this shortcut was defined

keymage('alt-c', function(e, ctx) {
    console.log(ctx.shortcut, ctx.scope, ctx.definitionScope);
});

// -> "alt-c", "", ""

Sequences

Keymage supports key sequences:

keymage('ctrl-k j', function() { alert("Nice!"); });

For this to fire you have to first press both ctrl and k, and then j. This will fire an alert.

There is something to remember: browsers have their own shortcuts, for example ctrl-j in most browsers means "open downloads". And while you can always call e.preventDefault() in usual situation, if ctrl-j is part of a sequence, it's not that easy - you'll get control over what's happening only when the whole sequence is pressed.

So keymage provides you with a means to support this use case. I do not encourage you to override browser hotkeys, but let's imagine you want to do that. For this, you can pass an option object as last parameter, having preventDefault property set to true:

keymage('ctrl-t ctrl-j k',
        function() { alert("wow"); },
        {preventDefault: true});

This option will prevent default on every key press which is a valid part of a bound sequence, including the one triggering your handler. Note that pressing only ctrl-j (without ctrl-t) will still open downloads, keymage looks for sequence of ctrl-t ctrl-j.

Scopes

Keymage support nested scopes. This means that your application can have few areas where you can gradually have more and more specific shortcuts. It works like this:

// You can skip scope argument if you want global work-always shortcut
keymage('ctrl-j q', function() { alert("Default scope"); });

// This will fire after "keymage.setScope('chat')"
keymage('chat', 'ctrl-j w', function() { alert("Chat scope"); });

// This will fire after "keymage.setScope('chat.input')"
keymage('chat.input', 'ctrl-j e', function() { alert("Chat.input scope"); });

You can control scopes with helpful pushScope and popScope methods. This way your nested view (or whatever is enabling nested scope) doesn't need to know about parent scope:

keymage.pushScope('chat') // scope is 'chat'

keymage.pushScope('input') // scope is 'chat.input'

keymage.popScope() // scope is 'chat'

keymage.pushScope('deep')
keymage.pushScope('deeper') // scope is 'chat.deep.deeper'

// way to jump out of deep scoping
keymage.popScope('chat') // scope is ''

pushScope returns resulting scope and popScope returns topmost scope it removed (so with parameters it's the one you've asked to remove).

Note that calling popScope with name of a scope which is repeated few times will pop topmost one, i.e.:

keymage.setScope('this.scope.is.deep.scope')
keymage.popScope('scope') // scope is 'this'

Options

Last and optional argument to keymage function is an option object. Here is a list of possible options:

• preventDefault: when true, calls event.preventDefault() on every key press which looks like a part of defined sequence.

• context: binding handler will be called with provided object as a context.

Unbinding

And if you ever need to unbind a handler, use this:

keymage.unbind('ctrl-j k', your_handler_function);

Also, keymage(...) returns a function, which unbinds this shortcut when called:

var unbinder = keymage('ctrl-j k', your_handler_function);
unbinder();