Set multiple const values based on conditional

Question

I want to set multiple values based on a conditional. This code would work:

let a;
let b;

if (fooBar) {
  a = "foo";
  b = "bar";
} else {
  a = "baz";
  b = "Hello world!";
}

But I am trying to adhere to FP (immutable variables) and DRY principles.

For one variable, I would do this:

const a = fooBar
  ? "foo"
  : "baz";

Can I somehow set multiple variables this way?

score 9 · Accepted Answer · answered Mar 27 '20 at 11:22

I would say nothing wrong with using let overall, however the answer to your question is:

const [a, b] = fooBar ? ["foo", "bar"] : ["baz", "Hello world!"]

In this case array destructuring can be used. So we create variables to access array item by index (a is #0, b is #1)

score 4 · Answer 2 · answered Mar 27 '20 at 11:21

4

Use a ternary to generate an object or array with the required values, then use destructuring to assign them:

const fooBar = false

const { a, b } = fooBar ? 
  { a: 'foo', b: 'bar' } 
  : 
  { a: 'baz', b: 'Hello world!' }
  
console.log(a, b)

answered Mar 27 '20 at 11:21

Ori Drori

Not a lot of saving in code here - it is actually larger than before – mplungjan Mar 27 '20 at 11:24
2

The request was immutable variables, not to save characters. – Ori Drori Mar 27 '20 at 11:26
Sure. But using an array destructe is so much simpler: `const [a, b] = foobar ? ["foo", "bar"] : ["baz", "Hello world!"];` – mplungjan Mar 27 '20 at 11:27
1

I like the more verbose option, that's not dependent or order, but I've mentioned the array option as well. – Ori Drori Mar 27 '20 at 11:29
1

@OriDrori DRY is also a requirement and this does not achieve that. – Toivo Säwén Mar 27 '20 at 11:32
1

The DRYness is in the logic and the assignment. The names of the properties are minor overhead. And again - I did mention arrays as an option. Use whatever you like. – Ori Drori Mar 27 '20 at 11:34

score 0 · Answer 3 · answered Mar 27 '20 at 11:28

0

I don't understand why everyone is so stuck at destructuring. Doesn't this work for you?

const a  = 1 ? 0 : -1,
      b = 0 ? 3 : -1;

answered Mar 27 '20 at 11:28

ibrahim tanyalcin

1

Does not fulfil DRY, the conditional needs to be written twice here. – Toivo Säwén Mar 27 '20 at 11:34
1. What if the two variables have independent conditions? 2. Noobish because you create an object in memory, and then cause 2 property access on top of 2 assignments and send it to garbage collection. DRY is not of any importance whatsoever in the situation of OP. – ibrahim tanyalcin Mar 27 '20 at 12:03
The question is specifcally related to if two values need to be set based on the same conditional. Otherwise I would use this solution. Cheers – Toivo Säwén Mar 27 '20 at 12:19

3 Answers3