Explain the TypeScript type where the keys of an object not found in an array should correspond to the type of another object

Question

Explain the TypeScript type where the keys of an object not found in an array should correspond to the type of another object

Currently, I am developing a utility function called copyKnownProperties that is responsible for copying properties from one class or object to another only if the key exists on both objects. In the example provided, you can observe an attempt to copy properties from B to A, and this execution is flawless in JavaScript.

I am seeking TypeScript to alert me when there is an attempt to copy properties with mismatched types. As seen in the scenario mentioned, both A and B share the same keys, but only the key foo has consistent type string across both objects. The implementation of this part is also successful.

The main challenge lies in evading this error by specifying the key within an array named omit. These keys will be excluded from the copying procedure, thereby eliminating the necessity of warning messages regarding their inconsistent types. However, conveying this information to TypeScript remains uncertain.

In short, my objective is to eliminate the error on line 27 due to the properties specified in the omit array.

[TypeScript Playground Source]

https://i.sstatic.net/JvAjJ.png

typescript typescript-generics

Answer 1

Answer №1

I made some slight adjustments to the solution provided by vr. and arrived at this revised version.

/**
 * This function copies properties from one object to another based on matching keys
 */
export function transferProperties<
  Target extends Partial<Omit<Source, ExcludedProps[number]>>,
  Source extends object,
  ExcludedProps extends (keyof Source)[] = [],
>(target: Target, source: Source, exclude?: ExcludedProps): Target {
  (Object.keys(target) as (keyof Target)[]).forEach((key) => {
    if (key in source && (!exclude || !exclude.includes(key as string as keyof Source))) {
      target[key as keyof Target] = source[
        key as string as keyof Source
      ] as unknown as Target[keyof Target];
    }
  });
  return target;
}

Answer 2

I made some slight adjustments to the solution provided by vr. and arrived at this revised version.

/**
 * This function copies properties from one object to another based on matching keys
 */
export function transferProperties<
  Target extends Partial<Omit<Source, ExcludedProps[number]>>,
  Source extends object,
  ExcludedProps extends (keyof Source)[] = [],
>(target: Target, source: Source, exclude?: ExcludedProps): Target {
  (Object.keys(target) as (keyof Target)[]).forEach((key) => {
    if (key in source && (!exclude || !exclude.includes(key as string as keyof Source))) {
      target[key as keyof Target] = source[
        key as string as keyof Source
      ] as unknown as Target[keyof Target];
    }
  });
  return target;
}

Explain the TypeScript type where the keys of an object not found in an array should correspond to the type of another object

Answer №1

Similar questions

Monitor changes in a dynamic child component using Angular fire and TypeScript only (no HTML)

Retrieve functions with varying signatures from another function with precise typing requirements

Using TypeScript to Verify the Existence of Words in a String

Guide on creating a decorator for asynchronous functions that runs exclusively when using `Promise.resolve()`?

Steps for implementing a conditional rendering in your codeHere is a

A more efficient method for defining and utilizing string enums in Typescript

How to utilize FileReader for parsing a JSON document?

Challenge with Updating React Components When Switching Themes

Setting an array of objects using TypeScript in the useState hook: A step-by-step guide

Encountering a Typescript error when attempting to access the 'submitter' property on type 'Event' in order to retrieve a value in a |REACT| application

I am unable to refresh the table data in Angular

Retrieving information from a .json file using TypeScript

Youngster listens for guardian's occurrence in Angular 2

Error: The default export is not a component compatible with React in the specified page: "/"

Navigating through async functions in an Express.js router

Next.js does not support tooltips with custom children components

What is the best way to delay a recursive JavaScript function for 3 seconds?

Creating a Dynamic Table with Angular 6 - Automating the Population of Content Values

Faulty deduction can occur when implementing the return statement in an identity function, or when incorporating an optional parameter

Error message: Cypress Vue component test fails due to the inability to import the Ref type (export named 'Ref' is missing)