What is the purpose of an empty value assignment in JavaScript (not null, undefined, etc)

I understand this:

let blah = null;
let blah = undefined;
let blah;

What I don’t understand is this:

    let obj = {}
      // notice the empty value assignment and the assignment that immediately follows
    obj.blah = 
    obj.blah = function(params) {
      // some code
    }

Is the empty assignment the same as let obj.blah;? I’ve seen this in a few npm packages where the key is provided a value directly beneath the empty value assignment of the same key. Is there a particular purpose to writing code this way? I’m refactoring a package to streamline its use, and I don’t want to simply delete this because of my ignorance. Any help will be greatly appreciated.

obj.blah = ( obj.blah = function () {} );