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Foundations · easy

1. What JavaScript runs on

Engines, the browser and Node.js.

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JavaScript is executed by an engine such as V8 (Chrome, Node.js, Bun) or JavaScriptCore (Safari). The language itself is small; most of what you use — the DOM, `fetch`, `window` — comes from the host environment.

js
console.log(typeof window); // "object" in a browser, "undefined" in Node

In Web3 work you write both: browser code that talks to a wallet, and Node code that talks to an RPC endpoint.

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Check your understanding

  1. 1. Which object is browser-only?

  2. 2. Which engine powers Node.js?

  3. 3. What is `fetch` part of?

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