Ever wanted to write horrible type-unsafe code without using 𝚊𝚗𝚢 or 𝚞𝚗𝚔𝚗𝚘𝚠𝚗 ?

DegenerateTypescript.ts

type Fruit = {
    name:      string
    color:     string
    sweetness: number
}

type Apple = Fruit & {
    variety: string
    color:   "red" | "green" | "yellow"
}

type Banana = Fruit & {
    length: number
    color:  "yellow"
}

type AppleAndBanana = [Apple, Banana]

function evil(both: Fruit[]) {
    const temp = both[0];
    both[0] = both[1];
    both[1] = temp;
}

const apple: Apple = {
    name:      "apple",
    color:     "red",
    sweetness: 7,
    variety:   "red delicious"
}

const banana: Banana = {
    name:      "banana",
    color:     "yellow",
    sweetness: 5,
    length:    6
}

const both: AppleAndBanana = [apple, banana];

evil(both); // technically no rules broken

console.log(both[1].length);  // undefined even though typescript says otherwise
console.log(both[0].variety); // ditto