Tests security awareness regarding dynamic code execution.
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Understand the problem
securitybest-practiceseval
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Attempt it yourself
Sketch your approach before reading the solution — that's what interviews test.
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Study the solution
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Give it an honest attempt first — then compare your thinking with the full walkthrough.
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Read the code
Replace eval with safe parsing / dispatch
// ❌ never: executes whatever the client sent
// const data = eval('(' + req.body + ')');
// ✅ parse data, don't execute it
const data = JSON.parse(req.body);
// ✅ choose behavior via a map, not generated code
const ops = { add: (a, b) => a + b, sub: (a, b) => a - b };
const fn = ops[req.query.op] ?? (() => { throw new Error('bad op'); });05
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