Javascript - flatMap method over array - (flatMap is not a function)

Question

According to the Mozilla Developer Website:

The flatMap() method first maps each element using a mapping function, then flattens the result into a new array. It

Answer 1

I was getting this when testing with jest, it's because flatmap is only part of node 11 and I was using node 10.

As a workaround, I added require('core-js/stable'); in my setupTests.ts.

I presume also there are some browsers that won't have this either. As such I will also put that require line in my application imports somewhere.