TypeScript (original) (raw)

TypeScript Version: 2.1.5

Code

function other() { return new Promise((resolve, reject) => { resolve("OK!"); }); }

function test(hosts: {whatever: boolean}[]) { let host = hosts.filter((f) => f.whatever).shift();

if (!host) { throw new Error("Crap!"); }

return other().then(() => { console.log(${host.whatever} selected); }); }

Playground

Expected behavior:

Do not emit an error about host possibly being null, since the method exits early if that's the case.

Actual behavior:

Typically when using strictnullchecks Typescript is intelligent enough to understand that when you throw an error from a method based on a type check/guard it narrows the type after the statement. As indicated in this short example:

function test(hosts: {whatever: boolean}[]) { let host = hosts.filter((f) => f.whatever).shift();

// Correctly calls out hose as possibly being null console.log(${host.whatever} selected);

if (!host) { throw new Error("Crap!"); }

// Does not complain here because of the above check/throw console.log(${host.whatever} selected); }

For some reason when you add the return of the function and use host through a closure it starts complaining.

I'm sure it's the closure, but I don't see how this could error.