Скачать или смотреть Manually Setting Value Object Properties in Typescript

Learn how to effectively set value object properties in Typescript when the data from a service call is null or unavailable. Get practical insights and examples to enhance your TypeScript skills.
---
This video is based on the question https://stackoverflow.com/q/69711018/ asked by the user 'Robert Mason' ( https://stackoverflow.com/u/17129498/ ) and on the answer https://stackoverflow.com/a/69711360/ provided by the user 'soylentthegreen' ( https://stackoverflow.com/u/14209733/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

Visit these links for original content and any more details, such as alternate solutions, latest updates/developments on topic, comments, revision history etc. For example, the original title of the Question was: Manually set value object's properties in typescript

Also, Content (except music) licensed under CC BY-SA https://meta.stackexchange.com/help/l...
The original Question post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license, and the original Answer post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license.

If anything seems off to you, please feel free to write me at vlogize [AT] gmail [DOT] com.
---
Manually Setting Value Object Properties in TypeScript: A Simple Guide

When working with TypeScript, especially within frameworks like Angular, you might encounter situations where your service calls return null or undefined data. This can lead to frustrations when you attempt to access properties of your data objects. In this guide, we will explore a common issue: how to safely set properties for a value object when the expected data is not available from a service call.

Understanding the Problem

You have a component that fetches house data from a service. The data structure you are dealing with includes an array of houses and their associated settings. However, when the service returns null, attempting to access or set properties on null objects results in an error: ERROR TypeError: Cannot set properties of null (setting 'dataList').

Here’s a snippet of your code where the issue arises:

[[See Video to Reveal this Text or Code Snippet]]

The line this.houseData.dataList = [...] throws an error when data is null because this.houseData itself is null. The goal is to ensure that houseData always has a default value.

Solution: Using Constructors with Default Values

The key to resolving this issue is to create a constructor in your classes that initializes the properties with sensible default values. This way, even if the service returns null, your component will have a reliable fallback.

Step 1: Modify Your Class Definitions

Update your HouseSettings, HouseResponse, and AllHouseData classes to include constructors with default parameters:

[[See Video to Reveal this Text or Code Snippet]]

Step 2: Safeguard Your Data Assignment

Now, you can streamline the assignment in your subscription method. Replace the current assignment logic with the nullish coalescing operator, ensuring that if data is null, a new instance of AllHouseData is created.

Here’s the updated subscription method:

[[See Video to Reveal this Text or Code Snippet]]

Summary

By implementing constructors with default values, you allow your TypeScript application to gracefully handle situations where data might be unavailable. This prevents runtime errors and ensures your application has a consistent state:

Check for null values: Always verify if the data coming from your service is null before accessing its properties.

Use default constructors: Set up your class constructors to initialize all properties to sensible default values.

Utilize safe assignment: Use the nullish coalescing operator (??) for assignments to ensure a fallback object is created when needed.

With these practices in place, you can enjoy smoother development in TypeScript and avoid common pitfalls when dealing with dynamic data from service calls.