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First of all I'm sorry if I get the jargon wrong, I'm new to typescript (I tried to search for this issue and failed, I may have used the wrong search terms).
When using type guards, code in an else block uses the condition in the if to infer the type of the variable. However if the if contains an early return the rest of the function should be treated as the else of the if from we we returned.
Code
// A self-contained demonstration of the problem follows...typeFoo={a: string};functionisFoo(x): x is Foo{returnx&&typeof(x.a)==='string';}typeBar={b: string};functionbuz1(arg: Foo|Bar) : string{if(isFoo(arg))returnarg.a;// OK arg inferred to be Fooelsereturnarg.b;// OK arg inferred to be Bar}functionbuz2(arg: Foo|Bar) : string{if(isFoo(arg))returnarg.a;// OK arg inferred to be Fooreturnarg.b;// ** Error b isn't a member of Foo|Bar **}
Expected behavior:
function buz2 should compile with no error. Actual behavior:
Error when accessing member b of arg even though arg can be inferred to be of type Bar (as it is in buz1.else).