Since I need to learn the ArcGIS Server JavaScript API, ESRI uses the JavaScript open source framework Dojo in this API, so I first learned some knowledge of Dojo to prepare for future work.
In fact, there are many open source JavaScript frameworks, such as the earliest prototype, the very practical jQuery, Yahoo's Yui, the stunning ExtJS, etc. As for why ESRI adopted Dojo, we don't have to guess. There must be someone who has a reason, so study hard. Dojo is the last word.
Before learning Dojo, you must master some necessary JavaScript knowledge, such as json, etc. Since I thought I could learn JavaScript well in the past, and I am just getting started with ExtJS, it is relatively easier to learn Dojo.
The latest version of Dojo is now version 1.5.0, and you can download the dojo-release-1.5.0.zip compressed file on its official website.
Getting back to the subject, here are some learning points for you, just treat it as a personal note.