Mastering `typeof` and `keyof` in TypeScript: Every Real-World Use You Need to Know

In this article, I’ll break down what `typeof` and `keyof` operators do, why they’re indispensable, and how you can use them like a pro. No fluff. Just the straight talk you need.

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What are typeof and keyofs are ?

• typeof is used to get the type of a variable or expression. It allows you to capture the type information of a value to reuse it elsewhere in your code.
• keyof is a type operator that extracts the keys of an object type as a union of string literal types. It’s useful for creating types based on the property names of an object.

Code Examples:

1. Extract type from a variable with typeof

const settings = { darkMode: true, version: 2 };
// Extract the type of 'settings' automatically


type SettingsType = typeof settings;

// SettingsType is:
// {
//   darkMode: boolean;
//   version: number;
// }

2. Get keys of a type with keyof

const settings = { darkMode: true, version: 2 };

type SettingsKeys = keyof SettingsType; 

// "darkMode" | "version"