Utils
Merge
Merges two types, where the second type overrides the first.
The Merge<FirstType, SecondType> utility type is designed to merge two object types together.
When encountering conflicting keys between the two types, the SecondType dictates the final property type, effectively overriding the FirstType.
Definition
Merge.ts
/**
* Merges two types, where the second type overrides the first.
*/
export type Merge<FirstType, SecondType> = Omit<FirstType, keyof SecondType> & SecondType;
Example Usage
This utility is extremely helpful when you are extending a base configuration or payload with specialized properties that might redefine existing properties.
example.ts
import type { Merge } from '@riavzon/utils'
interface DefaultConfig {
url: string;
timeout: number;
headers: Record<string, string>;
}
interface CustomConfig {
timeout: string; // Changed from number to string
retries: number; // New property
}
// Standard Intersection keeps `timeout` as `number & string` (which evaluates to `never`)
type BadIntersection = DefaultConfig & CustomConfig;
// Merge correctly overrides `timeout` to be `string`
type FinalConfig = Merge<DefaultConfig, CustomConfig>;
const config: FinalConfig = {
url: 'https://api.example.com',
timeout: '5000ms', // Allowed, because it was overridden to string
headers: { 'Content-Type': 'application/json' },
retries: 3
};
