Features of TypeScript

TypeScript combines JavaScript compatibility with editor assistance, type inference, useful type abstractions and incremental adoption.

In this lesson, you will study the rule, run a complete TypeScript example, explain its output, and test a small change.

Its main advantages include autocomplete from known types, safer refactoring, checking function arguments, and expressing object shapes with interfaces or type aliases. Type inference reduces annotation noise. TypeScript integrates with the JavaScript ecosystem; it does not guarantee correctness, and its types do not automatically exist at runtime.

Use the diagram to locate the checks, values or branches involved in the example.

Save this code as main.ts or paste it into the TypeScript Playground. The example uses fixed values so it runs without prompting for input.

TypeScript code

type Product = { name: string; price: number };
 const book: Product = { name: "Notebook", price: 80 };
 console.log(`${book.name}: ${book.price}`);

Verified output

Notebook: 80

How to run locally: npx tsc --strict --target es2022 --module commonjs main.ts, then node main.js. When using a project configuration, run the matching project build instead.

Product expresses a shape containing name and price. The assignment is checked for those properties. The program reads the same ordinary JavaScript object when it runs.

Predict the output before you run the sample. Compare each line with the source expression that produced it, and distinguish the type checker’s work from what happens in JavaScript at runtime.

An interface or type alias is not a runtime validator. Data obtained from JSON must still be checked when trust boundaries matter.

Debugging habit: when a change is rejected, read the exact compiler diagnostic and inspect the operand types. When it compiles but behaves unexpectedly, follow the values through the JavaScript expressions.

Add an inStock boolean property to Product and update book. Check what error appears if you omit the new required property.

Challenge: write down your prediction first, run the changed source, and explain any difference. Return to the verified version before continuing.

Features of TypeScript: Its main advantages include autocomplete from known types, safer refactoring, checking function arguments, and expressing object shapes with interfaces or type aliases.

Inference lets you keep source concise while retaining checking where sufficient information exists.

Before continuing, be able to explain what is checked before execution and what actually changes at runtime in the example above.