Swap key with value JSON

Question

I have an extremely large JSON object structured like this:

{A : 1, B : 2, C : 3, D : 4}

I need a function that can swap the values with

Answer 1

Now that we have Object.fromEntries:

obj => Object.fromEntries(Object.entries(obj).map(a => a.reverse()))

or

obj => Object.fromEntries(Object.entries(obj).map(([k, v]) => [v, k]))

(Updated to remove superfluous parentheses - thanks @devin-g-rhode)