define(type [, defaultAttributes, prototypeProperties, staticProperties])

Helper to define a new Cell class or extend an existing one.

The type must be a unique identifier of the class, which determines the location of the class definition in the joint.shapes namespace (type is the path to the class definition delimited by dots: .). When creating an instance of the cell, attributes will be set to the value from the defaultAttributes, unless overridden by subclass or instance attributes.

// Define a new Ellipse class in `joint.shapes.examples` namespace
// Inherits from generic Element class
var Ellipse = joint.dia.Element.define('examples.Ellipse', {
    // default attributes
    markup: [{
        tagName: 'ellipse',
        selector: 'ellipse' // not necessary but faster
    attrs: {
        ellipse: {
            fill: 'white',
            stroke: 'black',
            strokeWidth: 4,
            refRx: .5,
            refRy: .5,
            refCx: .5,
            refCy: .5

// Instantiate an element
var ellipse = (new Ellipse()).position(100, 100).size(120, 50).addTo(graph);

// Define a new ColoredEllipse class
// Inherits from Ellipse
var ColoredEllipse = Ellipse.define('examples.ColoredEllipse', {
    // overridden Ellipse default attributes
    // other Ellipse attributes preserved
    attrs: {
        ellipse: {
            fill: 'lightgray'
}, {
    // prototype properties
    // accessible on `this.(...)` - as well as, more precisely, `this.prototype.(...)`
    // useful for custom methods that need access to this instance
    // shared by all instances of the class
    randomizeStrokeColor: function() {
        var randomColor = '#' + ('000000' + Math.floor(Math.random() * 16777215).toString(16)).slice(-6);
        return this.attr('ellipse/stroke', randomColor);
}, {
    // static properties
    // accessible on `this.constructor.(...)`
    // useful for custom methods and constants that do not need an instance to operate
    // however, a new set of static properties is generated every time the constructor is called
    // (try to only use static properties if absolutely necessary)
    createRandom: function() {
        return (new ColoredEllipse()).randomizeStrokeColor();

// Instantiate an element
var coloredEllipse = ColoredEllipse.createRandom().position(300, 100).size(120, 50).addTo(graph);