Neat deep merge using TypeScript generics

merge-example.ts

import { mergeObjects } from "./merge";

const defaultOptions = {
    userMedia: {
        audio: true,
        video: false,
        channelCount: 1,
        autoGainControl: true,
        echoCancellation: true,
        noiseSuppression: true
    },
    mediaRecorder: {
        mimeType: 'audio/webm; codecs="opus"',
        audioBitsPerSecond: 24 * 1024,
    },
    timeslice: 10,
    blob: {
        type: "audio/webm"
    },
    enableVoiceFeedback: true
};

const overridenOptions = mergeObjects(defaultOptions, {
    mediaRecorder: {
        audioBitsPerSecond: 96 * 1024,
    },
});

merge.ts

// Type-safe object merge implementation from https://spin.atomicobject.com/2018/05/14/type-safe-object-merging-2-8/
// Uses TypeScript's built-in utility types (See https://www.typescriptlang.org/docs/handbook/utility-types.html)

type Defined<T> = T extends undefined ? never : T;
type MergedProperties<U, T> = { [K in keyof T & keyof U]: undefined extends T[K] ? Defined<T[K] | U[K]> : T[K] };
type MinusKeys<T, U> = Pick<T, Exclude<keyof T, keyof U>>

export const mergeObjects = <T extends object, U extends object>(t: T, u: U) => ({
    ...(t as object),
    ...(u as object)
} as MinusKeys<T, U> & MinusKeys<U, T> & MergedProperties<U, T>);