How to create an array if an array does not exist yet?

Question

How do I create an array if it does not exist yet? In other words how to default a variable to an empty array?

Answer 1

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

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/isArray

Or if x could be an array and you want to make sure it is one:

const list = [].concat(x);

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/concat