merge designed for Webpack

 webpack-merge provides a merge function
 that concatenates arrays and merges objects
 creating a new object.
 If functions are encountered,
 it will execute them, run the results through the algorithm,
 and then wrap the returned values within a function again.
 .
 This behavior is particularly useful in configuring webpack
 although it has uses beyond it.
 Whenever you need to merge configuration objects,
 webpack-merge can come in handy.
 .
 There's also a webpack specific merge variant
 known as merge.smart
 that's able to take webpack specifics into account
 (i.e., it can flatten loader definitions).