How to convert an object which can be array or single object to an array in javascript

I have an object like below

const foo = (x : Array<string> | string) {
   ...
}

Now I want to treat x always as an array, I have done this

const y = Array.isArray(x) ? x : [x];

I know I can have another function to do this, looking for some built-in javascript function.

(this is simplified version I am doing this multiple times try to DRY)

>Solution :

You can use [].concat() or wrap the item with an array, and then flatten it:

const fn1 = x => [].concat(x)

console.log(fn1({ a: 1 }))
console.log(fn1([{ a: 1 }]))

const fn2 = x => [x].flat()

console.log(fn2({ b: 2 }))
console.log(fn2([{ b: 2 }]))

If the function only has a single parameter, you can use rest params, and flatten the array of arguments:

const fn = (...x) => x.flat()

console.log(fn({ a: 1 }))
console.log(fn([{ a: 1 }]))