When to use them ?

“If you can't explain it to a six year old, you don't understand it yourself.” ― Albert Einstein

I want to understand when to those properties, methods, libraries, frameworks...

Why use 'WHEN' ?

Some times we were asked like below questions:

• What is Flow or Why we need Flow

• What is TypeScript or Why we need TypeScript

• What is RxJs or Why we need RxJS

But, I don't like those questions.

I like questions as below:

• When we use Flow

• When we use TypeScript

• When we use RxJS

Because, when we know when to use a new stuff, that's the time we really understand it.