TypeScript for JavaScript Developers

# TypeScript for JavaScript Developers TypeScript is JavaScript with a type system layered on top. Every valid JavaScript file is close to valid TypeScript — the shift is mostly about adding type information, not learning a new language. ## Basic Types ```typescript let name: string = "Aarav"; let age: number = 24; let isEnrolled: boolean = true; ``` ## Typing Functions ```typescript function calculateFee(base: number, discount: number): number { return base - discount; } ``` Typed function parameters and return values catch a huge class of bugs at compile time instead of runtime. ## Interfaces for Object Shapes ```typescript interface Student { name: string; course: string; enrolled: boolean; } ``` Interfaces describe the shape of data flowing through your app — API responses, component props, function arguments. ## Type Inference TypeScript doesn't require annotating everything. It infers types automatically in most cases: ```typescript let count = 0; // inferred as number ``` Over-annotating obvious types adds noise without benefit. ## Common Early Mistakes New TypeScript developers often reach for `any` to silence errors quickly, which defeats the purpose of using TypeScript at all. Using `unknown` instead forces you to narrow the type before using it safely. ## Gradual Adoption TypeScript can be introduced file-by-file into an existing JavaScript project using `allowJs`, so teams don't need a full rewrite to start benefiting from it. ## Conclusion TypeScript's real value shows up in larger codebases and teams, where catching type mismatches at compile time prevents entire categories of production bugs before they ship.