Define an optional variable

[alex3165]

This is a proposal, I would like to be able to define an optional variable which automatically set the type to the variable of type T or undefined.

Currently we can only define optional function parameter or object property.

TypeScript Version: 2.1.1 / nightly (2.2.0-dev.201xxxxx)

Code

  const getParams = (state: State): NextState | undefined => (state.blabla || undefined)
  const prevParams?: NextState | undefined = getParams(state);

Expected behavior:

  const getParams = (state: State): NextState | undefined => (state.blabla || undefined)
  const prevParams?: NextState = getParams(state);

(Inspired from Swift)

[RyanCavanaugh]

Duplicate #13321. Please search before logging new issues.