Coding⏱️ 2 min read📅 2026-05-31

How to Fix: TypeScript: Index signature is missing in type

TypeScript error explanation and solution.

Quick Answer: The issue is that the interface MyInterface does not have an index signature, which means it cannot be used as a dictionary. To fix this, add the index signature to the interface definition.

📋 Table of Contents

  1. ✅ Best Solutions to Fix It
  2. 🎯 Final Words

The error 'Index signature is missing in type' occurs when TypeScript cannot find an index signature for a given type. In your case, the issue arises from the fact that you have defined `MyInterface` with a generic object `{ [name: string]: number }`, but when creating an instance of it (`let o = { ... }`), you're missing the type annotation for the property names.

✅ Best Solutions to Fix It

Method 1: Add Index Signature Type Annotation

  1. Step 1: Update the `MyInterface` definition to include an index signature type annotation, like so:
interface MyInterface { dic: T; }

By adding the `` type annotation, we're telling TypeScript that `MyInterface` expects an object with a property named 'dic' whose value is of type `{ [name: string]: number }`. This will allow you to create instances of `MyInterface` without any issues.

🎯 Final Words

In summary, the solution lies in adding an index signature type annotation to your `MyInterface` definition. This will ensure that TypeScript can correctly infer the properties of your objects and prevent errors like 'Index signature is missing in type'.

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