While working in Javascipt we need to quickly append semi-colons to most lines. These settings modify Atom to map command-; to add a semi-colon to the end of the current line.
In init.coffee:
atom.commands.add 'atom-text-editor', 'custom:semicolonize', ->
editor = @getModel()
editor.moveToEndOfLine()
editor.insertText(';')
In keymap.cson
'atom-workspace atom-text-editor':
'cmd-;': 'custom:semicolonize'