Strange syntax error with map and arrow functions

Question

Never seen this one before:

.flatMap(obj => {
        return removeOneLine(this)
            .map(l => {l:l,id:obj.id});

I want to map the result, but of course, I guess JS doesn't know if this is an object or the function body.

Is doing the following the only way to avoid a syntax error (because it's ambiguous to the engine):

  .flatMap(obj => {
           return removeOneLine(this)
                .map(l => {
                    return {l: l, id: obj.id}
                });
        })

is this ambiguity in this situation normal, any way to mitigate besides what I just did above?

Btw, you changed two things in your code, you removed the `return` keyword. It's unclear if that's just a "typo" or part of your actual change. Either way it's completely unrelated to the problem. — Felix Kling, Dec 29 '16 at 06:03
sorry, I didn't mean to remove that return statement, edited, thanks — Alexander Mills, Dec 29 '16 at 06:05

Mark Reed · Accepted Answer · 2016-12-29T06:07:49.057

1

Why do you have the curlies for a single-statement fat-arrow function?

You don't need curly braces around the function bodies or an explicit return statement. You do, however, need to put parentheses around the object literal to prevent its being interpreted as a function body.

.flatMap( obj=> removeOneLine(this).map(l => ({ l: l, id: obj.id })) )

edited Dec 29 '16 at 06:07

answered Dec 29 '16 at 06:03

Mark Reed

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I guess because I wanted to put it on multiple lines? I guess it works even if I put it on multiple lines, idk – Alexander Mills Dec 29 '16 at 06:04
You might want to explain what you changed instead of asking a (rather unrelated) question ;) – Felix Kling Dec 29 '16 at 06:05
@FelixKling huh? :) this was all about the answer given by Mark, and it is a duplicate question – Alexander Mills Dec 29 '16 at 06:07
aka, this does answer the question http://stackoverflow.com/questions/28770415/ecmascript6-arrow-function-that-returns-an-object – Alexander Mills Dec 29 '16 at 06:07
1

Fair enough, I updated my answer, but you're right, it's a dupe. – Mark Reed Dec 29 '16 at 06:08
@AlexanderMills: My comment was directed at Mark, not you. – Felix Kling Dec 29 '16 at 06:08
ahh, got it sorry about that – Alexander Mills Dec 29 '16 at 06:14

Strange syntax error with map and arrow functions

1 Answers1