👀 Views: 973 💬 Answers: 1 📅 Created: 2025-06-09

typescript generic-types utility-types

After trying multiple solutions online, I still can't figure this out. I'm trying to create a utility function in TypeScript that can perform a deep merge on two objects while preserving their types. I want to ensure that the resulting object has the merged types of both input objects. I wrote a function like this: ```typescript function deepMerge<T, U>(target: T, source: U): T & U { const merged = { ...target }; for (const key in source) { if (source.hasOwnProperty(key)) { const value = source[key]; if (typeof value === 'object' && value !== null && !Array.isArray(value)) { merged[key] = deepMerge(merged[key] || {}, value); } else { merged[key] = value; } } } return merged; } ``` However, I'm working with a type scenario when I try to merge two objects of different shapes. For instance: ```typescript const obj1 = { a: 1, b: { c: 2 } }; const obj2 = { b: { d: 3 }, e: 4 }; const merged = deepMerge(obj1, obj2); ``` In my IDE, I'm seeing an scenario where `merged` is inferred as `{ a: number; b: { c: number; d: number; }; e: number; }` which is fine, but when I try to access `merged.a` later, TypeScript gives me an behavior saying `Property 'a' does not exist on type 'never'.` I've also tried defining the return type of the function explicitly, but that doesn't seem to resolve the scenario: ```typescript function deepMerge<T extends object, U extends object>(target: T, source: U): T & U { // function body } ``` What am I missing? Is there a better way to handle deep merges in TypeScript while ensuring type safety? This is my first time working with Typescript LTS. Any pointers in the right direction?