return object from array map

Question

Suppose I could hardcode the following:

const data = [ { a: 0, b: 1}, {a:2,b:3},... ]

But I have the data in an array, and I would like to write something like the following:

const data = my_arr.map((element,index) => { a:element, b:index});

How does one yield this kind of object from an array map?

Answer 1

You just need to add parenthesis around the returned object literal.

const my_arr = [1,2,3,4,5];
const data = my_arr.map((element, index) => ({ a: element, b:index }));
//                                          ^                       ^    

console.log(data);

The reason is that the JavaScript parser rules assume that the { following the => is the start of a function body. To go around this, we wrap the object in () (alternatively we can add a return statement)

Read more here: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Functions/Arrow_functions#Returning_object_literals