What do parenthesis surrounding brackets in the return statement of an ES6 arrow function do?

Question

For example in redux actions, I\'ve seen in someone\'s code:

export const updateMessage = text => {
   return (dispatch) => {
     dispatch(updateChatMess         


        

Answer 1

As per the arrow function docs,

// Parenthesize the body of a function to return an object literal expression:

params => ({foo: bar})

That means if you want to return an object implicitly you have to wrap it in parentheses.

Without this, code inside braces will be considered as function body and not an object (as you'd want)

Following are equivalent:

params => { return {foo: bar}} // Explicitly return an object (from function body)
params => ({foo: bar}) // Implicitly return an object by wrapping it with parentheses

Answer 2

In the first example, the {} are used to identify multiple lines of code, which is why the return is required in order to obtain something other than undefined.

In the second example, the {} are used to create an object.

Answer 3

when you write myFunction = value => ({prop: value}) it return the object {prop: value}, in this case {} are object delimiter and not 'function delimiter'

const updateChatMessage = text => ({
   type: types.someActionType,
   text
})

another eg :

when you want to multiply by two each elem of an array you can write :

array.map(elem => {return elem * 2})

or

array.map(elem => elem * 2) //same result

and if you want an eg with () that wrap an object litteral :

let array = [{val: 2},
             {val: 4},
             {val: 8},
             {val: 16}];
             
let output = array.map( ({val}) => ({val: val*2}) );

console.log(output);

Answer 4

If you wrap the brackets with parenthesis you are making your function return an object literal (thus you don't need the return keyword). If you don't use parenthesis you have to use the return keyword.