What is meaning of domain and default function in javascript? -

what meaning of defaults: function($super) , domain: function($super) in javascript?. following code taken openstack-horizon. using high level of javascript concept know basic of javascript.

rickshaw.graph.renderer.staticaxes = rickshaw.class.create(rickshaw.graph.renderer.line, {         name: 'staticaxes',   defaults: function($super) {     alert("13 => repeated many time. rickshaw.graph.renderer.staticaxes");     return rickshaw.extend($super(), {       xmin: undefined,       xmax: undefined,       ymin: undefined,       ymax: undefined     });   },   domain: function($super) {     //alert("hj");     var ret = $super();     var xmin, xmax;     // if y axis wants have static range, not based on data     if (this.ymin !== undefined && this.ymax !== undefined) {       ret.y = [this.ymin, this.ymax];     }     // if x axis wants have static range, not based on data     if (this.xmin !== undefined && this.xmax !== undefined) {       xmin = d3.time.format.utc('%y-%m-%dt%h:%m:%s').parse(this.xmin);       xmin = xmin.gettime() / 1000;       xmax = d3.time.format.utc('%y-%m-%dt%h:%m:%s').parse(this.xmax);       xmax = xmax.gettime() / 1000;        ret.x = [xmin, xmax];     }     return ret;   } }); 

consider code.

var objectliteral = {     variable: "i'm string",     fun: function(param) {         console.log("i'm function.");         console.log("here's param: ", param);     } }  console.log(objectliteral); objectliteral.fun(); 

fun , variable fields of object literal.
function() syntax used declare function, assigned fun.