Conditional chaining in JavaScript or TypeScript

Question

Is there a syntax to add a function to a chain under conditions?

In this example, I would like myKey to be Joi.string().required() if modifier === true, but just Joi.string() if it is false:

function customJoi(modifier) {
  return Joi.object({
    myKey: Joi.string() //#If(modifier) .required() #EndIf
  });
}

I know I could do without this feature, with multiple steps. I'm just wondering if there is a nice way to write it concisely for large objects.

@Touffy :shrug: OP states "conditional chaining" which seems to describe the problem pretty well and the question elaborates; IMO it's fine. — Dave Newton
– Dave Newton, Commented Jan 3, 2022 at 17:23
I agree, once you read it carefully it's a good description. But who reads carefully nowadays ? (see first comment on this post…). Maybe just write "optional" in italics or something ? — Touffy
– Touffy, Commented Jan 3, 2022 at 17:29
@Touffy I think most people who answered and commented here did read correctly :) — Seeven
– Seeven, Commented Jan 3, 2022 at 17:31
@Touffy My bad - happens sometimes to me - hope I get pardoned.. ;) — iLuvLogix
– iLuvLogix, Commented Jan 3, 2022 at 17:33

Ankh · Accepted Answer · 2022-01-31 12:27:26Z

8

You could take optional, if not required.

myKey: Joi.string()[modifier ? 'required' : 'optional']()

edited Jan 31, 2022 at 12:27

Ankh

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answered Jan 3, 2022 at 17:18

Nina Scholz

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2 Comments

Seeven Over a year ago

Thanks, I think that's the best we can get :) Although one limitation is that you have to have a fallback method for the ternary operator to work, as undefined doesn't seem to be acceptable.

Touffy Over a year ago

True. Though I guess in a controlled environment you could define a "noop" method on any chainable you design, so you always have that option. Or… gasp… define it on Object.prototype and be despised by all your coworkers.

GenericUser · Accepted Answer · 2022-01-03 17:14:37Z

5

You can achieve that with a ternary.

function customJoi(modifier) {
    return Joi.object({
        myKey: modifier ? Joi.string().required() : Joi.string()
    });
}

answered Jan 3, 2022 at 17:14

GenericUser

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1 Comment

Seeven Over a year ago

Thanks, it's a good answer too, but I'll accept Nina Scholz's answer because it's closer to what I was looking for, especially for longer chains. Although one advantage of your method is you don't need a fallback method for the ternary operator.

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