dynamic-return.ts

type Test = {
    foo: number
    returnString?: boolean
}

function test(): number
function test(arg: Omit<Test, 'returnString'>): number
function test(arg: Test & { returnString: false }): number
function test(arg: Test & { returnString: true }): string
function test(arg: Test = { foo: 2 }): number | string {
    if (arg && arg.returnString) {
        return ''
    }
    return 0
}

const t1: number = test()
const t2: number = test({
    foo: 1
})
const t3: number = test({ returnString: false, foo: 1 })
const t4: string = test({ returnString: true, foo: 2 })