When declaring a type alias, I encountered an issue where I could not initialize it without creating an item:
type ModelState = [string, string[]];const modelState: ModelState = [null,[]];modelState["firstName"] = ["First name is required."];If I try to initialize like this:
const modelState: ModelState = [];I get an error in TypeScript stating "Type 'undefined[]' is not assignable to type '[string, string[]]'". What would be the correct way to handle this situation?
It is recommended to initialize the tuple with data, but you can bypass this by tricking the compiler in the following way:
const modelState: ModelState = [] as any;
A tuple in the format of [string, string[]] will still be treated as an array with a numerical index. It seems like what you really need is something like this:
interface ModelState {
firstName: string[],
lastName: string[],
}
Alternatively, you could consider structuring it like this:
interface ModelState {
[key: string]: string[],
}
There are some issues with initializing in this manner:
const modelState: ModelState = [] as any;Consider adding a key value pair:
modelState["firstName"] = ["First name is required."];console.log(JSON.stringify(modelState));The resulting JSON object appears to be empty.
However, when initialized differently and the key/value pair is added, it functions as intended.
const modelState: ModelState = {};In addition, TypeScript will flag an error if the value is not an array of strings. It does not raise an issue if the key is not a string though.
It may not seem intuitive at first, but it does work.
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