Create SharePoint project
Check _references.js file
You open the _references.js file and you can see some reference directives in the form of XML comment as the following:
So now, you can use JSOM intelliSense in the current project. But sometimes, you don’t know why the JSOM intelliSense stop working without any noticed from Visual Studio. Then you search Google and find out the way that just restarting your Visual Studio then the problem is solved. Another problem is you try to restart your Visual Studio but it is still not working. So then?
The best way that I’m following is downloading all reference files in your local, then add them to my SharePoint project. After that, I just need to change the path of those files in _references.js:
There you go! Now just do happy coding.