Existe uma maneira de mapear o Sublime Text para tratar o mjs como js?
Veja a seguinte resposta do StackOverflow:
In the current version of Sublime Text 2 (Build: 2139), you can set the syntax for all files of a certain file extension using an option in the menu bar. Open a file with the extension you want to set a default for and navigate through the following menus:
View -> Syntax -> Open all with current extension as... ->[your syntax choice].Updated 2012-06-28: Recent builds of Sublime Text 2 (at least since Build 2181) have allowed the syntax to be set by clicking the current syntax type in the lower right corner of the window. This will open the syntax selection menu with the option to
Open all with current extension as...at the top of the menu.Updated 2016-04-19: As of now, this also works for Sublime Text 3.
Fonte Defina a sintaxe padrão para o tipo de arquivo diferente em Sublime Text 2 , responda por Colin R