Therefore:

1 - this.mutation = this.get // returns this.get

2 - this.query = <return value of this.mutation = this.get, which is this.get>

3 - this.patch = <return value of this.query = this.mutation = this.get, which is this.get>

n - and so on...

Essentially, it's setting 6 different properties all to the same value.

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EDIT: Here's the same concept, but in a different context...

function fibonacci(num, memo = {}) {

    if (num <= 1) return 1;

    if (memo[num]) return memo[num];

    return memo[num] = fibonacci(num - 1, memo) + fibonacci(num - 2, memo);

On the return line, the right-to-left property of "=" forces the extreme right to be processed first. It returns the recursive call.

Then, the return value of this recursive call gets saved to "memo[num]".

Finally, the return value of "memo[num] = fibonacci(...) + fibonacci(...)", which is still the same return value from the recursive call, gets saved to the function return.

Like if you wanted to return a empty hash {} for:

  GET /
  DELETE /
  PUT /
  PATCH /
  POST /