#9 most askedVery commonMediumWeb security

Cross-site scripting (XSS)

🏢 Asked in real interviews

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What is XSS, and how do you prevent it?

🎤 Answer it out loud, then check yourself

Say your answer as if the interviewer is listening (30–90 seconds). Then reveal what a strong answer covers and tick what you said.

const comment = '<img src=x onerror="alert(document.cookie)">';
const escape = (s) => s.replace(/[&<>"']/g, (c) => ({ "&": "&amp;", "<": "&lt;", ">": "&gt;", '"': "&quot;", "'": "&#39;" })[c]);
console.log(escape(comment));

Answer out loud first, then compare.

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