Approach to do error handling in typescript

errorHandling.ts

// Usually one wowuld import these declerations like such
// import { ok, err, Result } from './util'
export declare type Result<T, E>
    = Ok<T, E> // contains a success value of type T
    | Err<T, E> // contains a failure value of type E

// utility functions to build Ok and Err instances
export declare const ok: <T, E>(value: T) => Ok<T, E>
export declare const err: <T, E>(err: E) => Err<T, E>
export declare class Ok<T, E> {
    readonly value: T
    constructor(value: T)
    isOk(): this is Ok<T, E>
    isErr(): this is Err<T, E>
}
export declare class Err<T, E> {
    readonly error: E
    constructor(error: E)
    isOk(): this is Ok<T, E>
    isErr(): this is Err<T, E>

}


// What is being returned from the API
type ResponseData = {
    statusCode: number
    responseBody?: Object
    addData: Object
    success: boolean
}

const api = {
    get: (url: string): ResponseData => {
        return { success: true, statusCode: 200, responseBody: { url: url }, addData: null }
    }
}

// This function could be located in API or APIReact
const bottomFunc = async (url: string): Promise<Result<ResponseData, Error>> => {
    try {
        const resp = await api.get(url)
        //responsibility of Developer to check what should be regarded an error and what not
        if (!resp.success || resp !== null) {
            return err(new Error(
                'Invalid string passed into `makeHttpRequest`. Expected a valid URL.'
            ))
        }
        resp.addData = { 'user': '0xx' }
        return ok(resp)
    } catch (e) {
        switch (e) {
            // case 'AlreadySentException':
            //     return ok('Already sent')
            default:
                return err(new Error(
                    'unexpected Error' + e
                ))
        }
    }
}

// This function could be located in API or APIReact
const middleFunc = async (url: string): Promise<Result<ResponseData, Error>> => {
    const result = await bottomFunc(url)
    return result
}

// This function could be located in Web
const topFunc = async () => {
    // we have a Result<ResponseData, Error>
    const result = await middleFunc('https://myUrl.doc')
    if (result.isOk()) {
        // do something with the success value like redirect
        console.log(result.value)
    } else {
        // do something with the failure value like display error on Form
        console.error(result.error)
    }
}

topFunc()