Lesson 2 +10 XP

Static vs Dynamic Typing

JavaScript is dynamically typed, meaning variable types are checked at runtime. TypeScript brings static typing, checking variable types during compilation.

Comparison Overview

Aspect	Dynamic Typing (JavaScript)	Static Typing (TypeScript)
Type Checking	Occurs at runtime	Occurs at compile time
Variable Reassignment	Variable can hold any type at any time	Variable has a fixed or constrained type
Bug Discovery	Users may trigger runtime errors	Developer discovers errors while editing
Build Step	No compilation needed	Compilation step required

Example Code Comparison

In JavaScript:

let user = "Alice";
user = 42; // Allowed in JS, can cause unexpected bugs downstream
console.log(user.toUpperCase()); // Runtime TypeError: user.toUpperCase is not a function

In TypeScript:

let user: string = "Alice";
user = 42; // Error: Type 'number' is not assignable to type 'string'.

TL;DR

Dynamic languages check types during execution; static languages check types during compilation.
Static typing catches bug classes like misspelled properties and null pointer references early.