JavaScript Playground

Run and tweak the code examples from this prep book. Everything executes in your own browser — no server, no account, and your code never leaves this machine.

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Example

// A closure keeps its own copy of `n` alive after counter() returns.
function counter() {
  let n = 0;
  return () => ++n;
}

const next = counter();
const other = counter();

console.log(next(), next(), next());
console.log("independent:", other());

Console

Ctrl / ⌘ + Enter to run

console.log output appears here. Press Run, or Ctrl / ⌘ + Enter.

Your code runs in a sandboxed frame with no access to this page or your data, and is kept in this browser between visits. For languages other than JavaScript, open the Programiz compiler in a new tab.

JavaScript Playground

Code editor

Console