How to Access JSON Properties with Hyphens or Numbers in TypeScript with Rollup

Overcome issues with accessing JSON properties containing hyphens or numbers in TypeScript when using Rollup for your Svelte application. Learn effective workarounds!
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This video is based on the question https://stackoverflow.com/q/66647178/ asked by the user 'Jhon1213' ( https://stackoverflow.com/u/13965346/ ) and on the answer https://stackoverflow.com/a/66647747/ provided by the user 'Tim' ( https://stackoverflow.com/u/4270311/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Understanding the Problem: Accessing JSON Properties in TypeScript

When working with large JSON files in TypeScript, especially within a Rollup setup for your Svelte application, you may run into unexpected behavior when accessing keys in your JSON objects. A common issue arises when the keys contain hyphens or numbers, leading to undefined results. This guide will shed light on this problem and provide you with clear strategies to effectively access those properties.

The Scenario

Let's consider a practical example. You have a JSON object that includes various keys, some of which look like this:

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

However, when attempting to access this key in TypeScript, you experience an undefined output. The core of the problem lies in how JavaScript (and by extension, TypeScript) handles keys that include characters such as hyphens.

The Technical Breakdown

Why Hyphens Create Issues

In JavaScript, keys with hyphens cannot be accessed using the dot notation (e.g., object.key-name), as hyphens are interpreted as subtraction operators. Instead, you must use the square bracket notation (e.g., object['key-name']). This holds true, but there’s another layer when using the Rollup JSON plugin.

Rollup's JSON Plugin Behavior

When you utilize the JSON plugin with Rollup, it modifies the keys in your JSON objects:

It strips the hyphens from keys.

It also changes the next character to uppercase. So, accessible-icon gets transformed into accessibleIcon.

This transformation is likely the reason you're encountering undefined values when accessing these keys.

The Solution: Accessing the Modified Keys

Using Correct Access Notation

Given this knowledge, you can access your JSON properties correctly by using the transposed key names. Here are the steps:

Import Your JSON File: Ensure you're importing the JSON file correctly with Rollup.

Cast the Import: Use a defined interface for the JSON structure to help mitigate TypeScript errors.

Access the Keys: Utilize the following pattern to access keys transformed by Rollup.

For example, if you previously attempted to access the property like this:

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

You should change it to:

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

A Practical Example

Here's a snippet of how you might implement this in TypeScript:

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

By applying the above adjustments, you should effectively access your JSON properties even when they contain hyphens or numbers.

Conclusion

Working with JSON properties in an environment like TypeScript with Rollup can be tricky, especially when handling keys with hyphens or numbers. By understanding how Rollup modifies these keys, you can adopt the right access methods to avoid undefined results. Implementing the square bracket notation and adapting to Rollup’s key transformation will empower you to work smoothly with your JSON data.

Happy coding! If you encounter more issues, feel free to reach out for further assistance!