javascript - Why can't I use Array.prototype.join.call as a callback of a Promise?

Question

I'm trying to run this code:

Promise.resolve([1, 2]).then(Array.prototype.join.call).then(console.log);

Answer 1

The Function.prototype.call() method is not a function. It needs a this reference.

"The call() method calls a function with a given this value and arguments provided individually."

You will need to pass the response directly to it, or just call:

response.join()

Working example

Promise.resolve([1, 2])
  .then(response => Array.prototype.join.call(response))
  .then(console.log)