ES modules and types

Last reviewed May 28, 2026 Content v20260528

Track mode

client_typescript

Means

In-browser TS

Reading

~1 min

Level

intermediate

This lesson

This lesson teaches ES modules and types—the ideas, syntax, and habits you need before moving on in TypeScript.

Without a solid grasp of ES modules and types, you will repeat mistakes in TypeScript exercises and on real pages or scripts.

You will apply ES modules and types in contexts like: Modern front-end apps, Node APIs, and any team that standardizes on TS-first tooling.

Write TypeScript, compile in the browser, run the emitted JavaScript, and check understanding with MCQs.

Toward the end of the track—use it to consolidate patterns before the capstone or summary lessons.

Use import / export in TS sources. Type-only imports: import type { User } erase completely in output.

The lesson playground runs single-file snippets—no import between files here.

Project layout

In real repos: src/index.ts exports public API; tests import types with import type to avoid circular value imports. Bundlers (Vite, esbuild) respect "moduleResolution": "bundler" in modern tsconfig.

Self-check

When should you use import type instead of import?

Tip: Use import type to avoid circular value imports in large codebases.

Playground

Runs in your browser in a sandboxed frame. Backend runners appear when this track’s profile allows them.

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