Js Object-Oriented Programming and Interface Definition

// Constructor.var Interface = function(name, methods) {    if(arguments.length != 2) {        throw new Error("Interface constructor called with " + arguments.length          + "arguments, but expected exactly 2.");    }        this.name = name;    this.methods = [];    for(var i = 0, len = methods.length; i < len; i++) {        if(typeof methods[i] !== 'string') {            throw new Error("Interface constructor expects method names to be "               + "passed in as a string.");        }        this.methods.push(methods[i]);            }    };    // Static class method.Interface.ensureImplements = function(object) {    if(arguments.length < 2) {        throw new Error("Function Interface.ensureImplements called with " +           arguments.length  + "arguments, but expected at least 2.");    }    for(var i = 1, len = arguments.length; i < len; i++) {        var interface = arguments[i];        if(interface.constructor !== Interface) {            throw new Error("Function Interface.ensureImplements expects arguments "                 + "two and above to be instances of Interface.");        }                for(var j = 0, methodsLen = interface.methods.length; j < methodsLen; j++) {            var method = interface.methods[j];            if(!object[method] || typeof object[method] !== 'function') {                throw new Error("Function Interface.ensureImplements: object "                   + "does not implement the " + interface.name                   + " interface. Method " + method + " was not found.");            }        }    } };