var extend = require("extend");
...

var extend = require("gamtiq/extend");
...

var extend = require("./path/to/dist/extend.js");
...

require(["extend"], function(extend) {
    ...
});

System.import("extend").then(function(extend) {
    ...
});

define(["path/to/dist/extend.js"], function(extend) {
    ...
});

var SuperClass = function(a, b) {
    ...
};
SuperClass.prototype.method1 = function(c, d, e) {
    ...
};
...
var SubClass = function(a, b) {
    ...
    SubClass.superconstructor.call(this, a, b);
    // or
    // SubClass.superconstructor.apply(this, arguments);
    ...
};
extend(SubClass, SuperClass);
...
SubClass.prototype.method1 = function(c, d, e) {
    ...
    SubClass.superclass.method1.call(this, c, d, e);
    // or
    // SubClass.superclass.method1.apply(this, arguments);
    ...
};
...
if (extend.isSubclass(SubClass, SuperClass)) {
    ...
}