ReactJS - Array Callback Return

Question

In this case, I'm making a sum of the object and its working just as I wanted to, the problem is the following message:

Expected to return a value in arrow function array-callback-return

Here is the code:

data.map((current,index, array) => {
    const prevVisitors = array[index - 1 ] ? array[index - 1].visitors : 0
    current.visitors += prevVisitors
})

What should I use as a return statement if there is nothing to be returned(Since it's only a modification of the props)? And in what cases this error is useful?

map works that you need to return the changed value so you can return current after you changed it, even if in these cases a forEach could be more suitable — quirimmo
– quirimmo, Commented Apr 30, 2018 at 13:00
I didn't thought that way, it's really a misuse of the map function, thanks! — Paliao
– Paliao, Commented Apr 30, 2018 at 13:09

Laura delgado · Accepted Answer · 2018-04-30 15:16:39Z

1

Your code should be

data.map((current,index, array) => {
    const prevVisitors = array[index - 1 ] ? array[index - 1].visitors : 0
    return current.visitors += prevVisitors
})

answered Apr 30, 2018 at 15:16

Laura delgado

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1 Comment

Paliao Over a year ago

Yes, I used this at first, but with the answer of @quirimmo I thought better, and use forEach it's a better practice than return the current value, thanks

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