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Lesson 16 - The Error Class And Try-Catch-Finally In JavaScript

In the previous lesson, Anonymous Objects And Prototypes In JavaScript, we explained anonymous objects and prototypes. In today's tutorial, we're going to look at how to handle error states in JavaScript.

Errors will often occur in our programs. I'm not referring to errors caused due to poorly written code, we can avoid such errors pretty well. I'm mainly referring to errors caused by input/output operations, often referred to as I/O. The most common culprits for these sort of errors are user inputs from a form, storage inputs, API inputs, and so on. In all of these cases, there is a user who can enter invalid input, or a service which can return invalid data. However, we won't let them crash our programs due to errors. Instead, we'll sanitize all of the vulnerable places in the program and inform the user about the situation.

Active Error Handling

The first approach of dealing with program errors is called active error handling. We'll map all of the vulnerable spots in the program and sanitize them with conditions. Let's consider a program determining the first and last names from a full name. The code might look something like this:

const fullName = "Carl Smith";
const parts = fullName.split(' ');
const firstName = parts[0];
const lastName = parts[1];
document.write(`First name: ${firstName}, last name: ${lastName}`);

The code splits the full name, such as "Cal Smith", using the split() method by spaces, thereby obtaining a string with the first and last name. Everything works as it should as long as a correct name is entered:


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This tutorial explains how to throw error states in JavaScript using the Error class, as well as the try, catch, and finally blocks.

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Article has been written for you by Štěpán Zavadil
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