How to Create a Generic Function in TypeScript for Checking Object Properties

Описание: Discover how to implement a TypeScript function that checks if a generic object contains properties defined in an array of strings. Learn the best practices and coding techniques.
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This video is based on the question https://stackoverflow.com/q/67519889/ asked by the user 'Filippo Rivolta' ( https://stackoverflow.com/u/2095053/ ) and on the answer https://stackoverflow.com/a/67520201/ provided by the user 'iz_' ( https://stackoverflow.com/u/10611983/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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How to Create a Generic Function in TypeScript for Checking Object Properties

When working with TypeScript, especially with object properties and generic types, you may encounter some challenges. Many developers want to create functions that can handle objects with varying properties but still maintain type safety. One common scenario is to check if a given object has specific properties identified by an array of string keys. In this guide, we will dig into a solution for this problem and break it down into easily digestible sections.

The Problem Statement

Let's consider a practical example. Imagine you have an array of strings that represents certain keys, like property names, and an object that potentially contains values corresponding to those keys. You want to create a function that can check whether these properties exist in the object and return their values accordingly.

Here’s our scenario:

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In this example, staticStrings holds the keys we want to check, and genObject is the object we will inspect.

However, using plain JavaScript, the implementation of this function is straightforward. The issue arises when translating this logic into TypeScript. You want to ensure that your function is flexible enough to work with any type of object while preserving type safety.

Proposed Solution

While you might think generics are required for this solution, there's a simple way to achieve the desired functionality in TypeScript by leveraging the built-in Record utility type.

Updated Function Implementation

Here is a modified implementation of the renderStaticStrings function that accommodates the requirements without the complex use of generics:

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

Breakdown of the Code

Function Declaration:

We start off with const renderStaticStrings = (staticStrings: string[]) => { ... }. This means our main function accepts an array of strings.

Using Record:

The parameter genObject is defined as Record<string, any>. This is a dynamic way to specify that genObject can have any string keys pointing to values of any type. It removes the need for explicitly defining a generic type.

Property Check and Mapping:

Inside the function, we use map() to iterate through the staticStrings. For each string (ss), we check if it exists as a property in genObject using hasOwnProperty().

If the property exists, we return the value; if it does not, we return null.

Usage Example

You can now call this function easily:

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

In the output, you'll see that it returns ['John Doe', null, null, null] since only the name property exists in genObject.

Conclusion

The provided implementation offers a flexible approach to creating a TypeScript function that checks if an object contains certain properties as defined in an array of string keys. With this method, you can maintain type safety without the complexity of generics.

Now you can confidently create reusable code while taking full advantage of TypeScript’s capabilities!

Happy coding!