TypeScript Playground

The TypeScript Playground lets you experiment with a small program in a browser, see diagnostics and inspect the emitted JavaScript.

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

Open typescriptlang.org/play, enter TypeScript code, and inspect the JavaScript result. The editor makes type feedback immediate, but demonstrations that depend on Node filesystem APIs or external packages need a suitable local project instead.

Use the official TypeScript Playground.

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 User = { name: string; points: number };
 const player: User = { name: "Ravi", points: 12 };
 console.log(`${player.name}: ${player.points}`);

Verified output

Ravi: 12

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.

The type defines the required object fields. Hover on player to inspect inferred information; the output uses the concrete object values.

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.

Playground success does not mean a program is production-ready. Runtime input, deployment settings and package versions still 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.

Paste the snippet into the Playground, replace points with a string to view the error, then restore it. Inspect the emitted JavaScript tab.

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

TypeScript Playground: Open typescriptlang.

The Playground is an online learning and experimentation environment.

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