Combining types and test for it in typescript

Let’s combine some types and test for them:

type Item = {

item: string,

index: number

}

type Another = Item & {

isVisible: boolean

}

const test: Another = {

item: "heh",

index: 3,

isVisible: true

}

type Receipt = {

total: number,

id: string

}

const isItem = (info: Receipt | Item): boolean => {

let res = (info as Item).item !== undefined;

return res;

}

const a: Item = {

item: "driver",

index: 3

}

const b: Another = {

item: "screw",

index: 8,

isVisible: false

}

const c: Receipt = {

total: 2434,

id: "FJSK2SJ242"

}

console.log(isItem(a)); // true

console.log(isItem(b)); // true

console.log(isItem(c)); // false