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ViewsHow to get the value of keys from an array of objects in Typescript?
I have the array:
const studyTypes = [
{
value: "ENG",
label: "ENG-RU",
},
{
value: "RU",
label: "RU-ENG",
},
];
And the state:
const [typeStudy, setTypeStudy] = React.useState<string>("ENG");
How can I specify in typescript that my typeStudy can only take one of the value from the studyTypes array instead of a <string>? In this case the typeStudy can be either "ENG" or "RU".
·
Juan Pablo Isaza
2 answers
Answer question0
If you could declare studyTypes as a const, it should be like this:
const studyTypes = [
{
value: "ENG",
label: "ENG-RU",
},
{
value: "RU",
label: "RU-ENG",
},
] as const; // as const is important for this step
type Value = typeof studyTypes[number]['value'];
const testValue: Value = "PQR" // This will throw a type error.
This will only work with Typescript v3.4 or greater.
Here's an example from my VSCode checking for lint errors:
·
Juan Pablo Isaza
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0
You can define a new type as literal type.
type TypeStudy = "ENG" | "RU";
and then
React.useState<TypeStudy>
·
Juan Pablo Isaza
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