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Functions with overloads don't automatically get types for their parameters #32037

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@fregante

TypeScript Version: 3.5.2

Search Terms:

noImplicitAny true
overloaded
inferred types

Code

I don't know the exact terms for what's happening in the first example. Are these parameters' "types being inferred"?

// `text` has type `string`window.alert=(text)=>{returnwindow.alert(text);}// Both parameters are `any`, because `addEventListener` has overloadswindow.addEventListener=(type,fn)=>{returnwindow.addEventListener(type,fn);}

Expected behavior:
They should follow these types from lib.dom.d.ts:

addEventListener<KextendskeyofWindowEventMap>(type: K,listener: (this: Window,ev: WindowEventMap[K])=>any,options?: boolean|AddEventListenerOptions): void;addEventListener(type: string,listener: EventListenerOrEventListenerObject,options?: boolean|AddEventListenerOptions): void;

Actual behavior:

Parameter 'type' implicitly has an 'any' type. ts(7006)
Parameter 'fn' implicitly has an 'any' type. ts(7006)

Playground Link:https://www.typescriptlang.org/play/#src=window.alert%20%3D%20(text)%20%3D%3E%20%7B%0D%0A%09return%20window.alert(text)%3B%0D%0A%7D%0D%0A%0D%0Awindow.addEventListener%20%3D%20(type%2C%20fn)%20%3D%3E%20%7B%0D%0A%09return%20window.addEventListener(type%2C%20fn)%3B%0D%0A%7D

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