单线转多线ES6胖箭Function？

Question

I'm learning ES6 fat arrow functions. What is the correct way to change this code, so as to be able to put another line, even const a = 100; in the place indicated so that I can add some more lines to this function?

IMAdded: (options, args) => ({
    IMAdded: {
        filter: newIM => true, *need to add another line here*
    },
}),

Update:

Here's ES6 code that runs:

const subscriptionManager = new SubscriptionManager({
    schema,
    pubsub,
    setupFunctions: {
        APPTAdded: (options, args) => ({
            APPTAdded: {
                filter: appointment => (true),
            },
        }),
});

I'd like to add some more lines into the code that returns true .

Answer 1

If you want to convert the following method into having more lines:

{
  filter: appointment => true
}

You have to add curly braces and a return statement:

{
  filter: appointment => {
    // ... add your other lines here
    return true;
  }
}

Answer 2

filter: appointment => true,
...

is (and parentheses aren't needed around true ) a shortcut for

filter: appointment => {
  return true;
},
...

which is a shortcut for

filter: function (appointment) {
  return true;
}.bind(this),
...

Any amount of lines can be added before return statement.

Answer 3

No braces or return needed if your function body is an expression which can span multiple lines (a ConciseBody in the spec)

{
  filter: appointment =>
    true &&
    false
}

Note: I was initially confused about the question (hence the EDIT), and thought it was about linebreaks in arrow functions in general . And, yes, they are allowed, but only after the arrow.
See also the ESLint rule implicit-arrow-linebreak , which lists this variant under "Correct code" (if configured "with the below option")