TypeScript - null versus undefined

Question

The TypeScript Coding Guidelines state

Use undefined. Do not use null

Having just read another article on ECMAScrip

Answer 1

I made some research few months ago and I came out with the fact that undefined must be prioritize using tslint rule 'no-null-keyword'.

I tried to change my codebase and I had some issues. Why? Because I'm using an API that return null for empty fields.

I struggled because of the tslint triple-equals rule.

if (returnedData === undefined) // will be false because returnedData is null

Which let you 2 options:

1) Add some parameters to your triple-equals rules.

"triple-equals": [true, "allow-null-check"] and do If (returnedData == null)

allow-null-check allow "==" for null

2) Use If (returnedData) instead but it checks if null/undefined/empty string or a zero