Gain insights into TypeScript's core concepts, from basics to advanced type checking and iterators. Learn about static typing and JS library support through practical, hands-on experience.

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If you’re looking to move beyond vanilla JavaScript and take your skills to the next level, then you’ve come to the right place. TypeScript is an in-demand language that sits on top of JavaScript. This means you can do everything you can in JavaScript with TypeScript, but also enjoy countless other perks including support for JS libraries, NPM, static typing, and much more.

In this course, you’ll start from the beginning and work your way up to more advanced concepts like type checking, iterators, and manipulating objects and arrays. You'll get a chance to get your hands dirty with plenty of real practice along the way.

For JavaScript developers, TypeScript is a must-know language, not only for today but also for years to come. Don't miss out.

Learn TypeScript: The Complete Course for Beginners

# The `in` operator explained
The `in` operator can narrow a type from a union. The left part of the operand is a string or a string literal. The right part is a union type. The result is a `Boolean` that returns `true` if the union contains the string and `false` if it doesn’t.

# Usage of the `in` operator explained

This lesson will look at how to use the in operator to narrow a type.


Introduction

The Basics of Variables

Comment

Enum

Generic Type

Functions

Mapped Type

Objects

Index Signature

Variables Advanced

Exception

Alias

Type Checking

Iterators

Manipulating Objects and Array

Sharing Code

Conclusion

How to Narrow a Type with the in Operator

The `in` operator explained

How to Narrow a Type with the in Operator

The in operator explained

The `in` operator explained