I declare a type alias but cannot initialize it without creating an item:
type ModelState = [string, string[]];
const modelState: ModelState = [null,[]];
modelState["firstName"] = ["First name is required."];
TypeScript gives me an error "Type 'undefined[]' is not assignable to type '[string, string[]]'" if I try to initialize like this:
const modelState: ModelState = [];
What is the correct way?
Ideally you should initialize the tupel with data, but you can trick the compiler like this:
const modelState: ModelState = [] as any;
A tupel in in the form of [string, string[]] would still be an array with numerical index though. It looks to me that you actuall want something like this:
interface ModelState {
firstName: string[],
lastName: string[],
}
Or maybe even like this:
interface ModelState {
[key: string]: string[],
}
const modelState: ModelState = [] as any; should solve the issue.Initializing like this has problems:
const modelState: ModelState = [] as any;
Try adding a key value pair:
modelState["firstName"] = ["First name is required."];
console.log(JSON.stringify(modelState));
The JSON object remains empty.
If I initialize like this and add the key/value it works as expected.
const modelState: ModelState = {};
Also typescript reports an error if the value is not an array of strings. Doesn't report a problem if the key is not a string however.
Not sure if I can say this is intuitive but it works.