Here is something I can accomplish:
const keys = {
"hi": {name: "ho"}
}
type U = [keyof typeof keys][0]; // "hi"
But can I also achieve the same with array values?
const data = [
{ name: "hi" }
];
type T = typeof data[0]["name"]; // string not "hi"
To ensure your data is immutable, simply add as const to it:
const newData = [
{ item: "apple" }
] as const;
If you omit as const, the data will be interpreted as Array<{item: string}>. Remember that for objects like keys, it is not required to use as const since it already infers as {apple: {item: string}}.
When working with arrays in TypeScript, the type inference can be tricky due to elements changing at runtime. In this case, to ensure proper type inference for the data array as Array<{ name: string }>, you need to explicitly set the type of the data array as readonly. By doing so, TS can correctly infer the type for the first element inside the data array as {name: "hi"}.
To resolve this issue, simply include as const after the definition of the data array.
const data = [
{name: "hi"}
] as const;
// By adding 'as const', TS will infer the type for data as readonly[{ readonly name: "hi";}]
For a demonstration, you can view the example in TypeScript playground
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