In uuid@3.x the Version 4 algorithm was exported as a default:

const uuid = require('uuid');
uuid(); // -> "2b0d20b0-6462-4738-abe6-413512e9fbf2"

In the current master this is no longer the case:

const uuid = require('uuid');
uuid(); // -> Uncaught TypeError: uuid is not a function
uuid.v4() // -> "ea58b65b-80c4-44c6-b482-6714c78ac43e"

The minimum we should probably do is describe this in the README and in the CHANGELOG.

I could also try to use the data from https://github.com/tc39/proposal-uuid/tree/master/analysis in order to try to figure out how much of a breakage removing the default export would be?!

What do you think about this breaking change @broofa?