Transpile Drupal Module/Theme ES6 to ES5 in PHPStorm

gistfile1.txt

In PHPStorm, go to Preferences > Tools > File Watchers
Click the plus sign to add a new watcher, and choose Babel

Set "Program" to the babel-cli executable. On OSX this might be /usr/local/bin/babel. 
Or, if babel-cli is installed in node_modules, you can use the version found in node_modules/.bin

Set "Arguments" to $FileDirRelativeToProjectRoot$/$FileNameWithoutAllExtensions$.es6.js --out-file $FileDirRelativeToProjectRoot$/$FileNameWithoutAllExtensions$.js

Set "Output Paths To Refresh" to
$FilePathRelativeToProjectRoot$/$FileNameWithoutAllExtensions$.es6.js:$FilePathRelativeToProjectRoot$/$FileNameWithoutAllExtensions$.js