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Trevor I. Lasn

Staff Software Engineer, Engineering Manager

JavaScript Import Attributes (ES2025)

Understanding the new import attributes syntax and why we can't rely on file extensions alone

JavaScript is getting a new feature that makes module imports more explicit and secure. Import Attributes add a way to pass metadata about any module we’re importing - whether it’s JSON, JavaScript, or other module types.

The Core Problem

On the web, file extensions don’t reliably indicate content. A server might return JavaScript when you’re expecting JSON:


The Solution: Import Attributes

Import Attributes create a contract between your code and the runtime. You explicitly declare what type of module you expect:

The syntax works consistently across different module contexts:


Why Import Attributes?

The core problem is security. On the web, file extensions don’t reliably indicate content. A URL ending in .json might actually serve JavaScript:

Import Attributes make our module system more explicit and secure. JSON modules can’t execute code - they’re pure data. When you mark a module with type: "json", you’re guaranteed to get either JSON data or an error, never executable code.

The most immediate impact is on JSON imports, where security is crucial:

This feature creates a foundation for safely handling different module types in JavaScript. When it lands in 2025, we’ll have a standard way to declare our expectations about modules across all JavaScript environments.

Think of it as adding type safety to your module imports - not for the data inside the modules, but for the modules themselves.

Sources

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This article was originally published on https://www.trevorlasn.com/blog/import-attributes-in-javascript. It was written by a human and polished using grammar tools for clarity.