Using Signal for DOM Events

When using MochiKit.Signal, do not use the browser's native event API. That means, no onclick="blah", no elem.addEventListener(...), and certainly no elem.attachEvent(...). This also means that MochiKit.DOM.addToCallStack and MochiKit.DOM.addLoadEvent should not be used in combination with this module.

Signals for DOM objects are named with the 'on' prefix, e.g.: 'onclick', 'onkeyup', etc.

When the signal fires, your slot will be called with one parameter, the custom event object.

Custom Event Objects for DOM events

Signals triggered by DOM events are called with a custom event object as a parameter. The custom event object presents a consistent view of the event across all supported platforms and browsers, and provides many conveniences not available even in a correct W3C implementation.

See the DOM Custom Event Object Reference for a detailed API description of this object.

If you find that you're accessing the native event for any reason, create a new ticket and we'll look into normalizing the behavior you're looking for.

Memory Usage

Any object that has connected slots (via connect()) is referenced by the Signal mechanism until it is disconnected via disconnect() or disconnectAll().

Signal does not leak. It registers an 'onunload' event that disconnects all objects on the page when the browser leaves the page. However, memory usage will grow during the page view for every connection made until it is disconnected. Even if the DOM object is removed from the document, it will still be referenced by Signal until it is explicitly disconnected.

In order to conserve memory during the page view, disconnectAll() any DOM elements that are about to be removed from the document.

Using Signal for non-DOM objects

Signals are triggered with the signal(src, 'signal', ...) function. Additional parameters passed to this are passed onto the connected slots. Explicit signals are not required for DOM events.

Slots that are connected to a signal are called in the following manner when that signal is signalled:

• If the slot was a single function, then it is called with this set to the object originating the signal with whatever parameters it was signalled with.
• If the slot was an object and a function, then it is called with this set to the object, and with whatever parameters it was signalled with.
• If the slot was an object and a string, then object[string] is called with the parameters to the signal.

Signal API Reference

connect(src, signal, dest[, func]):

Connects a signal to a slot, and return a unique identifier that can be used to disconnect that signal.

src is the object that has the signal. You may pass in a string, in which case, it is interpreted as an id for an HTML element.

signal is a string that represents a signal name. If 'src' is an HTML Element, window, or the document, then it can be one of the 'on-XYZ' events. You must include the 'on' prefix, and it must be all lower-case.

dest and func describe the slot, or the action to take when the signal is triggered.

• If dest is an object and func is a string, then dest[func].apply(dest, ...) will be called when the signal is signalled.
• If dest is an object and func is a function, then func.apply(dest, ...) will be called when the signal is signalled.
• If func is undefined and dest is a function, then func.apply(src, ...) will be called when the signal is signalled.

No other combinations are allowed and will raise an exception.

The return value can be passed to disconnect to disconnect the signal.

disconnect(ident):

To disconnect a signal, pass its ident returned by connect(). This is similar to how the browser's setTimeout and clearTimeout works.

disconnectAll(src[, signal, ...]):

disconnectAll(src) removes all signals from src.

disconnectAll(src, 'onmousedown', 'mySignal') will remove all 'onmousedown' and 'mySignal' signals from src.

signal(src, signal, ...):

This will signal a signal, passing whatever additional parameters on to the connected slots. src and signal are the same as for connect().

DOM Custom Event Object Reference

event():

The native event produced by the browser. You should not need to use this.

src():

The element that this signal is connected to.

type():

The event type ('click', 'mouseover', 'keypress', etc.) as a string. Does not include the 'on' prefix.

target():

The element that triggered the event. This may be a child of src().

modifier():

Returns {shift, ctrl, meta, alt, any}, where each property is true if its respective modifier key was pressed, false otherwise. any is true if any modifier is pressed, false otherwise.

stopPropagation():

Works like W3C's stopPropagation().

preventDefault():

Works like W3C's preventDefault().

stop():

Shortcut that calls stopPropagation() and preventDefault().

key():

Returns {code, string}.

Use 'onkeydown' and 'onkeyup' handlers to detect control characters such as 'KEY_F1'. Use the 'onkeypressed' handler to detect "printable" characters, such as 'é'.

When a user presses F1, in 'onkeydown' and 'onkeyup' this method returns {code: 122, string: 'KEY_F1'}. In 'onkeypress', it returns {code: 0, string: ''}.

If a user presses Shift+2 on a US keyboard, this method returns {code: 50, string: 'KEY_2'} in 'onkeydown' and 'onkeyup'. In 'onkeypress', it returns {code: 64, string: '@'}.

See _specialKeys in the source code for a comprehensive list of control characters.

mouse():

Properties for 'onmouse*', 'onclick', 'ondblclick', and 'oncontextmenu':

• page is a MochiKit.DOM.Coordinates object that represents the cursor position relative to the HTML document. Equivalent to pageX and pageY in Safari, Mozilla, and Opera.
• client is a MochiKit.DOM.Coordinates object that represents the cursor position relative to the visible portion of the HTML document. Equivalent to clientX and clientY on all browsers.

Properties for 'onmouseup', 'onmousedown', 'onclick', and 'ondblclick':

• mouse().button returns {left, right, middle} where each property is true if the mouse button was pressed, false otherwise.

Known browser bugs:

• Current versions of Safari won't signal 'ondblclick' when attached via connect() (Safari Bug 7790).

• Mac browsers don't report right-click consistently. Firefox signals the slot and sets modifier().ctrl to true, Opera signals the slot and sets modifier().meta to true, and Safari doesn't signal the slot at all (Safari Bug 6595).

  To find a right-click in Safari, Firefox, and IE, you can connect an element to 'oncontextmenu'. This doesn't work in Opera.

relatedTarget():

Returns the document element that the mouse has moved to. This is generated for 'onmouseover' and 'onmouseout' events.