TypeScript/tests/baselines/reference/narrowingTypeofFunction.types at 5b00a7265fc79120c53bdc64c7737b570e4cefe7 · microsoft/TypeScript · GitHub

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=== tests/cases/compiler/narrowingTypeofFunction.ts ===
type Meta = { foo: string }
>Meta : Meta
>foo : string

interface F { (): string }

function f1(a: (F & Meta) | string) {
>f1 : (a: (F & Meta) | string) => void
>a : string | (F & Meta)

    if (typeof a === "function") {
>typeof a === "function" : boolean
>typeof a : "string" | "number" | "bigint" | "boolean" | "symbol" | "undefined" | "object" | "function"
>a : string | (F & Meta)
>"function" : "function"

        a;
>a : F & Meta
    }
    else {
        a;
>a : string
    }
}

function f2<T>(x: (T & F) | T & string) {
>f2 : <T>(x: (T & F) | (T & string)) => void
>x : (T & F) | (T & string)

    if (typeof x === "function") {
>typeof x === "function" : boolean
>typeof x : "string" | "number" | "bigint" | "boolean" | "symbol" | "undefined" | "object" | "function"
>x : (T & F) | (T & string)
>"function" : "function"

        x;
>x : (T & F) | (T & string)
    }
    else {
        x;
>x : T & string
    }
}

function f3(x: { _foo: number } & number) {
>f3 : (x: {    _foo: number;} & number) => void
>x : { _foo: number; } & number
>_foo : number

    if (typeof x === "function") {
>typeof x === "function" : boolean
>typeof x : "string" | "number" | "bigint" | "boolean" | "symbol" | "undefined" | "object" | "function"
>x : { _foo: number; } & number
>"function" : "function"

        x;
>x : never
    }
}