Quick Answer

Attempting to invoke a non-function value

Understanding the Issue

TypeScript prevents calling values that aren't functions. This error occurs when trying to invoke something that doesn't have a call signature.

The Problem

This code demonstrates the issue:

Typescript Error 
// Problem: Calling non-function
const name = "Alice";
name(); // Error

The Solution

Here's the corrected code:

Typescript Fixed 
// Solution 1: Call actual function
function greet() { ... }
greet();

// Solution 2: Check type before calling
if (typeof name === "function") {
    name();
}

// Solution 3: Fix type declarations
type Callable = () => void;
const func: Callable = () => console.log("Hello");

Key Takeaways

Only invoke values that are declared as functions.