Run CoffeeScript 2 online — compiles to JavaScript. Sandboxed, no install.
CoffeeScript compiles to JavaScript with a lighter syntax influenced by Ruby and Python. Historic Rails ecosystem staple, still used in some codebases, still worth learning if you want to see the shape of ES6 sugar before ES6 shipped.
ls-judge compiles your .coffee source and runs the emitted JS on Node inside a Firecracker microVM.
Clicking "Run now" opens the playground with this exact code and a matching test case pre-loaded — passes on first Run.
lines = []
process.stdin.on 'data', (d) -> lines.push d.toString()
process.stdin.on 'end', ->
n = parseInt lines.join('').trim()
process.stdout.write "#{n*2}\n"
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