What does fn mean when used in Raphael?

I saw a fn use in raphael, which is a javascript lab.

Raphael.fn.g.piechart = function (cx, cy, r, values, opts) {
  // blah...blah
}

it extend raphael, so people can uses like r = Rap开发者_开发知识库hael; r.g.piechart.

I search google and have nothing seem to be clear my mind. hope you help.

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fn is used for adding your own methods to the canvas.

Any methods you add to fn will work on the canvas. This is in contrast to methods that would work on for example an element ( for which you would use el).

Since extending the fn object will act on the canvas, you must add your custom methods before creating your Raphael instance (this is not true if you are extending the el of an element).

For example, from the documentation:

  // Extend Raphael fn object by adding methods to it:
Raphael.fn.arrow = function (x1, y1, x2, y2, size) {
    return this.path( ... );
}; 
  // or add namespaces to it:
Raphael.fn.mystuff = {
    arrow: function () {…},
    star: function () {…},
    // etc…
};

  // Now when you create a Raphael instance, your custom
  // methods are available.
var paper = Raphael(10, 10, 630, 480);

  // Using custom methods:
paper.arrow(10, 10, 30, 30, 5).attr({fill: "#f00"});

  // Using name spaced custom methods
paper.mystuff.arrow();
paper.mystuff.star();

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Update (thanks AleksandraKos):

Note that, namespaced plugins was removed in Raphael 2.0

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Initially it's just an empty object created along with Raphael, it's literally just:

Raphael.fn = {};

It's a common place for plugins to be stored, and they're called from there when a new instance is created.

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In your own JS code It can be whatever you want - it's not a reserved word, it doesn't have any special meaning, so you can name variable or method fn just like you can use names like foo or myVariable. In jQuery, for example, jQuery.fn === jQuery.prototype (a shortcut for plugin authors).

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Its short for function.

Its used as a namespace which Raphael stores all its functions under, which automatically allows you apply these functions to a paper object.

You can also extend the functionally of Raphael by adding functions to it.

This is similar to how jQuery's $.fn works.

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fn is nothing special in JavaScript. It's just the name of a property Raphael uses. See http://raphaeljs.com/reference.html

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Nothing special with fn in JavaScript.