# 20 Mistakes That Quietly Destroy JavaScript/TypeScript Codebases (Part 1)

DevFeed: [20 Mistakes That Quietly Destroy JavaScript/TypeScript Codebases (Part 1)](<https://devfeed.tech/articles/20-mistakes-that-quietly-destroy-javascript-typescript-codebases-part-1-18102.md>)

Original publisher: [Read original article](<https://thetshaped.dev/p/20-mistakes-that-quietly-destroy-javascript-typescript-codebases-common-code-smell-patterns>)

Author: The T-Shaped Dev

Published: 2026-05-02T02:19:25Z

Content type: tutorial

Language: en

Sources: [The T-Shaped Dev](<https://devfeed.tech/sources/the-t-shaped-dev.md>)

Topics: [JavaScript](<https://devfeed.tech/topics/javascript.md>), [TypeScript](<https://devfeed.tech/topics/typescript.md>), [Code](<https://devfeed.tech/topics/code.md>), [modern web development](<https://devfeed.tech/topics/modern-web-development.md>)

Tags: [bugs](<https://devfeed.tech/tags/bugs.md>), [code](<https://devfeed.tech/tags/code.md>), [javascript](<https://devfeed.tech/tags/javascript.md>), [mistakes](<https://devfeed.tech/tags/mistakes.md>), [patterns](<https://devfeed.tech/tags/patterns.md>), [typescript](<https://devfeed.tech/tags/typescript.md>)

## AI overview

This tutorial examines common JavaScript and TypeScript codebase mistakes that increase maintenance costs without necessarily breaking builds or tests. Part 1 focuses on type modeling, error handling, and module design, including TypeScript strict mode and unsafe type escapes.

## Source excerpt

Common JS/TS patterns that feel fine until they don't. 11 mistakes, before/after code for each. (11 min)