Since CommonJS, multiple module formats have emerged for client-side applications, such as AMD and UMD. AMD, or Asynchronous Module Definition, is an early fork of the CommonJS format, and supports asynchronous module loading. This means modules that do not depend on each other can be loaded in parallel, partially alleviating the slow startup time that clients face if they use CommonJS on the browser.
Whenever there are multiple unofficial standards, someone will usually come up with a new standard that's supposed to unify them all:
From the XKCD comic titled "Standards" (https://xkcd.com/927/); used with permission ...
