What is the process of transforming an array of string variables into TypeScript types?

I am inquiring about the process of converting an array of string variables to TypeScript types.

It is worth noting that there are two existing SO answers addressing this issue, but they involve passing strings hardcoded to maintain their original values.

  • How to convert array of strings to typescript types?
  • Convert array of strings to TypeScript type

Both solutions pass an array directly to preserve string values as literals. However, when passing an array as a variable, it fails to function correctly.

Using inline values works.

https://codesandbox.io/s/30y547yl91 https://i.sstatic.net/g9HcY.png

However, using variable values does not work.

https://codesandbox.io/s/qrrq24k7q https://i.sstatic.net/JLuja.png

Question

So, how can one create a type that restricts a list of allowable string values in domElements as a variable to asLiterals?

arraystypescript

Answer №1

Whenever an array literal gets assigned to a variable, it automatically widens to conform with expected behavior.

As a result, the variable named elements is now categorized as type string[] instead of ('b' | 'section' | ...)[]

The solution lies within your codebase. Implement a function similar to asList() in order to generate a contextualized array.

export function createLiteralArray<U extends KeyTypes>(...values: U[]): U[] {
    return values
}

This functionality can also be accessed through the type-helper library.

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