# Bug Report <!-- Please fill in each section completely. Thank you! --> ### π Search Terms <!-- What search terms did you use when trying to find an existing bug report? List them here so people in the future can find this one more easily. --> expression not callable union arrays ### π Version & Regression Information This changed between versions 4.1.3 and 4.2 beta ### β― Playground Link https://www.typescriptlang.org/play?ts=4.1.3#code/CYUwxgNghgTiAEYD2A7AzgF3gDwFzxQFcBbAIxBgG0BdeAH3kxgEsUBzGgKE+wDpioABwAUAM3gBeAHzxRASiA https://www.typescriptlang.org/play?ts=4.2.0-beta#code/CYUwxgNghgTiAEYD2A7AzgF3gDwFzxQFcBbAIxBgG0BdeAH3kxgEsUBzGgKE+wDpioABwAUAM3gBeAHzxRASiA ### π» Code ```ts declare const x: number[] | string[] x.map(f => f) ``` ### π Actual behavior `.map` is now callable but `f` as an implicit type of `any`, leading to an implicit any error. ### π Expected behavior The current behaviour in 4.1.3 is to mark the `map()` call as not callable as well as `f` should have an implicit any type. I don't know if this is a regression but I'm raising it because this change in behaviour is not documented in the release notes.