typescript-ifArray-conditional-return

ifArray.ts

type AnyArray = any[];
type NotArray = Exclude<any, AnyArray>;

//#region ifArray

//#region Definition

function ifArray<T, F, O extends Array<any> = Array<any>>(obj: O, isTrue: T, isFalse: F): T;
function ifArray<T, F, O extends Exclude<any, any[]>>(obj: O, isTrue: T, isFalse: F): F;
function ifArray<T, F, O>(obj: O, isTrue: T, isFalse: F): T | F 
{ 
    if(Array.isArray(obj)) return isTrue; else return isFalse; 
}

//#endregion Definition

//#region Testing

{ 

//#region Constants

const IS_ARRAY:     Array<number> = [1,2,4,5,5,]
const IS_NOT_ARRAY: object        = { notArray: "FFFF" };
const IS_NUM:       number        = 5;
const IS_STR:       string        = "F";

//#region Test Shape / Declaration

interface ReturnObj 
{ 
    (prop: any): 5; "5": Window
}; 
const RET_OBJ = Object.assign(
    function(prop: any){ return 5 }, 
    {
        '5': window 
    }
);

//#endregion Test Shape / Declaration

//#endregion Constants

//#region Tests

//#test Return String
{
    let TRUE_STR:       string = ifArray(IS_ARRAY,      IS_STR, IS_NUM);
    //@ts-expect-error
    let ERR_TRUE_STR:   string = ifArray(IS_ARRAY,      IS_NUM, IS_STR);

    let FALSE_STR:      string = ifArray(IS_NOT_ARRAY,  IS_NUM, IS_STR);
    //@ts-expect-error
    let ERR_FALSE_STR:  string = ifArray(IS_ARRAY,      IS_NUM, IS_STR);
}

//#test Return Object
{
    let TRUE_STR:       ReturnObj = ifArray(IS_ARRAY,      RET_OBJ, IS_NUM);
    //@ts-expect-error
    let ERR_TRUE_STR:   ReturnObj = ifArray(IS_ARRAY,      IS_NUM, RET_OBJ);

    let FALSE_STR:      ReturnObj = ifArray(IS_NOT_ARRAY,  IS_NUM, RET_OBJ);
    //@ts-expect-error
    let ERR_FALSE_STR:  ReturnObj = ifArray(IS_ARRAY,      IS_NUM, RET_OBJ);
}

//#endregion Tests

}

//#endregion Testing

//#endregion ifArray