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Type Inference in for... in combined with typeof #12944
Description
TypeScript Version: 2.1.4
The following code gives an error in TS 2.1:
It's not really nice code, but I think it should work never the less :)
for (var a in this) {
if (typeof this[a] === "function" && !ko.isObservable(this[a]))
this[a] = this[a].bind(this);
}Expected behavior:
I would expect this[a] to be typed as this[keyof this] & Function:
for (var a in this) {
if (typeof this[a] === "function" && !ko.isObservable(this[a]))
this[a] =( <this[keyof this] & Function> this[a]).bind(this);
}Actual behavior:
It gives an error, as of TS 2.1, it worked in TS 2.0 (because mapped types did not exist, this[a] was typed as any)
Activity
ahejlsberg commentedon Dec 15, 2016
I think the suggestion here is that a
typeof x === "function"type guard should change the type ofxto(typeof x) & Functionunder the guard. We currently do something similar for primitive types, but nothing specific for functions.