Errors

Security notes, SOC lab write-ups and tested code by Mahir Faysal, a SOC Level 1 cybersecurity learner in Bangladesh, plus notes from my Next.js and Gemini projects. Sample posts are marked and drafts stay in the admin area.

All notes Coding tips · 140 Learning notes · 25 Practice · 1

Coding tips

TypeError: Cannot read properties of undefined (reading 'x') in JavaScript: 10 Causes and Fixes (Tested Examples)

"Cannot read properties of undefined (reading 'x')" means the thing before the dot is undefined, not that x is missing. Find which value is undefined, then fix the cause: data not loaded yet, a missing return, a typo in a key, an array index past the end, or a lost this.

October 31, 2026 · 15 min read · 1 view