How to return a spread operator in a map arrow function in one line

Question

What I need to do is map over an Array and set a value to false on all of the objects. This was my first shot:

data = data.map((item) => {
  item.active = false;
  return item;
})

Works! But then there is Eslint, no-param-reassign. So I had to find something else. After some googling I found the spread operator! Awesome! I created this masterpiece:

data = data.map((item) => {
  return {...item, active: false}
})

Looks cool and works as well. But then there is Eslint again, arrow-body-style. ok fine I will return the object on the same line:

data = data.map(item => {...item, active: false});

Dosn't work! :'( Am I missing something?

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/forEach — TheCrzyMan, Jul 25 '18 at 12:43
I don't think this closing is right. The real problem wasn't returning an object from a lambda. — Denys Séguret, Jul 25 '18 at 12:50
@DenysSéguret It's unclear what the real problem is and what the OP really needs, the whole question he asked revolves around mapping an array to an array of new objects. — Bergi, Jul 25 '18 at 12:53

Denys Séguret · Accepted Answer · 2018-07-25T12:48:36.990

27

When returning a literal object from an arrow function construct (a lambda), you have to wrap it in parentheses so that it's seen as an expression:

data.map(item => ({...item, active: false}));

map is only useful if you need a different array.

But there's a simpler solution here. You don't have to reassign all items and data. You should simply do

data.forEach(item => item.active=false)

edited Jul 25 '18 at 12:48

answered Jul 25 '18 at 12:42

Denys Séguret

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I knew that I was missing something. Thanks that worked – Justin Lek Jul 25 '18 at 12:49
That probably still breaks the *no-param-reassign* rule. You should rather do `for (const item of data) item.active = false;` – Bergi Jul 25 '18 at 12:50
Yes it indeed still breaks the rule. but then there is the next one https://eslint.org/docs/rules/no-restricted-syntax – Justin Lek Jul 25 '18 at 12:58
Are there any downsides to the first example with wrapped parantheses? – Prof Jun 12 '21 at 14:14

How to return a spread operator in a map arrow function in one line

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