Quick Answer

Attempting to use a namespace as a type

Understanding the Issue

In TypeScript, namespaces and types are distinct concepts. This error occurs when you try to use a namespace (container of code) where a type is expected.

The Problem

This code demonstrates the issue:

Typescript Error 
// Problem: Using namespace as type
namespace MyNamespace {
    export function demo() {}
}
let x: MyNamespace; // Error

The Solution

Here's the corrected code:

Typescript Fixed 
// Solution 1: Export a type
namespace MyNamespace {
    export interface MyType {}
}
let x: MyNamespace.MyType; // OK

// Solution 2: Use typeof for values
const y: typeof MyNamespace.demo; // OK

Key Takeaways

Ensure you reference actual types, not namespaces, in type annotations.