javascript - Confusion with how thenable callback works in Promise?

Question

I am new to JS and was learning promises. The code excerpt I want to show is this

promisedFunction.then(data=>console.log(data))

or simply

promisedFunction.then(console.log)

which is equivalent of the former code excerpt. The question is how is that possible to just use then(console.log) instead of then(data=>console.log(data))? Does it mean that we can omit the passed-from-promise data in thenable callback?

Answer 1

data=>console.log(data) is a function that takes a parameter and calls a method with the passed in argument.

If you pass console.log it will execute the same method and still pass the same argument.

In effect you are dropping the extra function call - slightly more abstractly, imagine this:

//some function `f`
const f = x => x + 1;

//different function `g` that just forwards the call to `f`:
const g = x => f(x);

console.log(g(41)); //42