Typescript array of arrays of arrays: protect from undefined

Question

I am parsing a complex object in Typescript, so have something like:

const a = reply['price']['value']['total']['value'];

and I like to ensure that all elements are defined in the chain, otherwise, it should set a=0 and do not trigger an exception if some of the chained keys are in fact undefined.

What would be the appropriate syntax for that?

nullptr · Accepted Answer · 2022-06-28 14:09:35Z

4

If you're using modern JS you can use nullish coalescing and optional chaining

const a = reply?.['price']?.['value']?.['total']?.['value'] ?? 0;

Try to avoid using || instead of ??, because that will give you 0, if the final value is any falsy value, like 0 or false.

If you don't want to use nullish coalescing, you can do this, which achieves the same.

const a = reply?.['price']?.['value']?.['total']?.['value'] ? reply['price']['value']['total']['value'] : 0;

answered Jun 28, 2022 at 14:09

nullptr

4,6442 gold badges20 silver badges49 bronze badges

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

2 Comments

Radu Diță Over a year ago

I think using || in this case is actually better. Considering the name is value, probably 0 is what you want and not false.

nullptr Over a year ago

I guess it could be reasoned that if the value is false, and we are checking for the value, false is what they actually want

l -_- l · Accepted Answer · 2022-06-28 14:32:16Z

0

If you can't use @nullptr 's answer, I suggest creating a function for that purpose :

function getObjectNestedValue2(obj, keys, defaultValue) {
    let currObjOrValue = obj;
    keys.forEach(key => {
        if (!currObjOrValue.hasOwnProperty(key)) {
            currObjOrValue = defaultValue;
            return;
        }
        currObjOrValue = currObjOrValue[key];
    });
    return currObjOrValue;
}

You then call it like so :

const a = getObjectNestedValue(reply, ['price', 'value', 'total', 'value'], 0);

Cheers

answered Jun 28, 2022 at 14:32

l -_- l

6767 silver badges18 bronze badges

1 Comment

nullptr Over a year ago

the question is tagged as typescript, so you'll have to provide the type for the function as well. the function you provided will throw errors if implicitAny is set to false

Collectives™ on Stack Overflow

Typescript array of arrays of arrays: protect from undefined

2 Answers 2

2 Comments

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

2 Comments

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related