CODEWITHSUNDEEP
javascripttypescript
Kousha
Kousha

Reputation: 36219

Typescript typecast existing variable

Say I'm using a module of the following type:

interface AwesomeLibrary {
    name: string;
    query: Object;
}

I want to typecast query into another interface:

interface Query {
    startDate: string;
    endDate: string;
    showAll: boolean;
}

Let's say there is a function callback that gives me the AwesomeLibrary. I want to then typecast the query into Query. Right now this is all I have:

functionCb(response: AwesomeLibrary) {
    // This works fine
    let query: Query = response.query as Query;
    // Now, query.startDate is available
    // Do stuff to query
    // At the end, I want to send response back to another function, so I do
    response.query = query;
    otherFunction(response);

    // This does not work, but basically what I want:
    response.query = response.query as Query;
    // Then do stuff to response.query directly
    // Here response.query.startDate is not available, instead I have to use response.query['startDate']

    // Even this does not work:
    let query: Query = response.query as Query;
    response.query = query;
}

Thoughts?

Upvotes: 0

Views: 109

Answers (1)

Nitzan Tomer
Nitzan Tomer

Reputation: 164147

You can type cast it like so:

(response.query as Query).startDate = (new Date()).toUTCString();

Or you can have another variable:

let response2 = response as AwesomeLibrary & { query: Query };
response2.query.startDate = (new Date()).toUTCString();

You can also receive the parameter in this type:

function functionCb(response: AwesomeLibrary & { query: Query }) {
    response.query.startDate = (new Date()).toUTCString();
}

But then you'll need to cast when calling this function.

Upvotes: 1

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