Cover by Nicholas C. Zakas

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Chapter 10. Throw Your Own Errors

When I was younger, the most befuddling part of programming languages was the ability to create errors. My first reaction to the throw operator in Java was, “Well, that’s stupid; why would you ever want to cause an error?” Errors were my enemy—something I sought to avoid—so the ability to cause an error seemed like a useless and dangerous aspect of the language. I thought it was dumb to include the same operator in JavaScript, a language that people just didn’t understand in the first place. Now, with a great deal of experience under my belt, I’m a big fan of throwing my own errors.

Throwing errors in JavaScript is an art. It takes time to feel out where the appropriate parts of your code should throw errors. Once you figure this out, however, you’ll find that your debugging time will decrease and your satisfaction with the code will increase.

The Nature of Errors

An error occurs in programming when something unexpected happens. Maybe the incorrect value was passed into a function or a mathematical operation had an invalid operand. Programming languages define a base set of rules that when deviated from, result in errors so that the developer can fix the code. Debugging would be nearly impossible if errors weren’t thrown and reported back to you. If everything failed silently, it would take you a long time to notice that there was an issue in the first place, let alone isolate and fix it. Errors are the friends of developers, not enemies.

The problem ...

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