Ch 12 · Error Handling · JavaScript

Topic 12 of 13 in JavaScript — Complete Tutorial (Beginner) — 2 lessons.

Why Errors Happen and Why They Matter

Programs deal with all kinds of unpredictable situations. A user might type a word where a number was expected. A calculation might divide by zero. A piece of data the program needs might not exist yet. These are called runtime errors — problems that only appear when the program is actually running, because they depend on data that changes as the program is used. If your program does not handle these situations, it will crash abruptly and show the user a confusing error message — a very poor experience.

Throwing Your Own Errors

You are not limited to handling errors that JavaScript or the system throws automatically — you can deliberately throw your own errors when your code detects an invalid or impossible situation. You do this with the throw keyword, followed by a new Error object containing a descriptive message that explains exactly what went wrong. This is an important technique for data validation: when a function receives input that violates its expected rules, throwing an error immediately — rather than silently continuing with bad data — makes problems visible and easy to debug.

All topics in JavaScript Beginner

1. Introduction to Programming & JavaScript
2. Your First JavaScript Program
3. Variables — Your Data Containers
4. Data Types — Kinds of Values
5. Operators & Expressions
6. Conditional Statements
7. Loops & Iterations
8. Functions
9. Arrays — Lists of Data
10. Objects & Classes
11. Strings — Working with Text
12. Error Handling
13. Mini-Projects & Practice