Log and Return

log.ts

export function log(): undefined;
export function log<T>(arg: T): T;
export function log<T extends readonly unknown[]>(...args: T): T;
export function log<T>(...args: T[]): T[] | T | undefined {
    console.log(...args);
    if (args.length === 0) return undefined;
    if (args.length === 1) return args[0];
    return args;
}
  
let a = log(5);
a // : number
let b = log({v: "Hola"})
b // : { v: string; }
let c = log()
c // : undefined
let d = log(1,2)
d // : [number, number]
let e = log([1,2])
e // : number[]
let f = log([1,2],[3,4])
f // : [number[], number[]]
let g = log(...[1,2,3, {a:5}])
g // : [number, number, number, { a: number}]
let h = log(...[1,2,3,4], ...[5,6,7,8])
h // : [number, number, number, number, number, number, number, number]

let val = Math.random() < 0.5 ? [1,2,3] : ['a','b','c']
let i = log(...val)
i // : number[] | string[]

let val2 = Math.random() < 0.5 ? [1,2,3,'a'] : ['a','b','c']
let j = log(...val2)
j // : (string|number)[]