How to use JavaScript lodash push to an array only if value doesn’t exist?

To use JavaScript lodash push to an array only if value doesn’t exist, we use sets.

For instance, we write

const s = new Set();

s.add("hello");
s.add("world");
s.add("hello");

to create a set with the Set constructor.

And then we call add to add 'hello' and 'world'.

'hello' won’t be added a 2nd time since it already exists.