If validation to check if value is Undefined

Question

If validation to check if value is Undefined

Asked 4 years, 10 months ago

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-1

I’m having trouble checking if the value is undefinded. I need to make a if for this validation, follow my code:

My interface:

interface IModalContatos {
  dados: IContatos | undefined;
  onSave:(dados: IContatos) => void;
  onClose:() => void;
}

Man state (state):

const [contatoAtualizado,setContatoAtualizado]=useState<IContatos>(dados as IContatos);

Validation:

useEffect(() => {
    if (dados === undefined) {
    }
    setContatoAtualizado(dados as IContatos)
}, [dados]);

I believe you wanted to return the data as Undefined when there is no iContatos, in this case is a double pipe: dados: IContatos || undefined;

– Ivan Ferrer

2020/12/08 at 18:53
You can also return this, it will result in boolean: true / false: return (!!IContatos);

– Ivan Ferrer

2020/12/08 at 18:55
I don’t quite understand what you want to do. Could you try [Edit] the question to clarify what your goal is? You just want to update the state if dados is different from undefined? Then it wouldn’t be enough to put the setContatoAtualizado(dados) within the if, also changing it to if (dados !== undefined) { ... }?

– Luiz Felipe

2020/12/09 at 15:02

1 answer

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by Victor Guedes • 56 points · Answer 1 · 2020-12-09T14:53:02+00:00

You can try using the operator typeof. For example :

if (typeof dados === "undefined")

Apparently every time undefined you want to run setContatoAtualizado right? If that’s what you can try to use on useEffect already passing this condition, something like:

useEffect(() => {
  if (typeof dados === "undefined"){
    setContatoAtualizado(dados as IContatos);
  }
}, [dados]);