What does this JavaScript code trying to do?

Question

I came across a block of code in a project and I find it hard to understand:

let isSelected = false;
const results = items.filter(Boolean).map(item => {
  isSelected = !isSelected && id === item.id;
  return {
    id: item.id,
    name: item.name
  };
});

What's the line isSelected = !isSelected && id === item.id; before the return is trying to do?

Thanks.

CertainPerformance · Accepted Answer · 2022-06-03 01:00:01Z

2

It's a confusing way of, while mapping through the array, also setting isSelected to true if any of the elements in the array match the ID.

An equivalent approach would be

const truthyItems = items.filter(Boolean);
const results = truthyItems.map(item => ({
  id: item.id,
  name: item.name
}));
const isSelected = truthyItems.some(item => item.id === id);

Side-effects inside a .map callback are usually a bit of a code smell.

answered Jun 3, 2022 at 1:00

CertainPerformance

373k55 gold badges354 silver badges359 bronze badges

Sign up to request clarification or add additional context in comments.

Collectives™ on Stack Overflow

What does this JavaScript code trying to do?

1 Answer 1

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Related