JavaScript Errors

Errors are unavoidable in programming, and JavaScript provides robust tools to handle them. Understanding how to handle errors effectively can save you hours of debugging and make your code more reliable.

Throw, and Try…Catch…Finally

The try…catch statement is used to handle exceptions. It lets you test a block of code for errors (try), handle the error (catch), and execute code, regardless of the result (finally).

Errors Will Happen!

JavaScript code often encounters issues due to incorrect inputs, syntax problems, or unexpected behavior. Handling errors gracefully ensures that your application doesn’t crash unexpectedly.

JavaScript try and catch

The syntax of a try…catch block:

Example:

try { // Code that may throw an error let result = someUndefinedFunction(); } catch (error) { console.error(‘An error occurred:’, error.message); }

JavaScript Throws Errors

JavaScript throws errors when something goes wrong. For example, accessing a property of undefined or calling a non-existent function will throw an error.

The throw Statement

The throw statement allows you to create custom errors. The error can be a JavaScript String, a Number, a Boolean or an Object.

Example:

function validateAge(age) { if (age < 18) { throw new Error('Age must be 18 or above'); } return true; } try { validateAge(15); } catch (error) { console.log(error.message); }

Input Validation Example

Input validation is a common use case for throw and try…catch.If the value is wrong, an exception (err) is thrown. For example, validating a user’s input in a form:

HTML Validation

Here’s how to combine HTML and JavaScript for validation:

Example:

The finally Statement

The finally block executes code after try and catch, regardless of the outcome.

Example:

The Error Object

JavaScript provides an Error object to represent runtime errors.

Name and message are two useful properties that are provided by the error object.

Error Object Properties
●
message: Describes the error name.
●
name: Type of error or error message (a string).

Error Name Values

EvalError

RangeError

ReferenceError

SyntaxError

TypeError

URIErrorr

Example:

EvalError

Occurs when the eval() function is used incorrectly.

Example:

RangeError

Occurs when a number falls outside of the legal value range.

Example:

ReferenceError

Occurs when accessing a variable that is undeclared.

Example:

SyntaxError

Occurs when the code has a syntax error.

Example:

TypeError

Occurs when a variable or parameter is not of a valid type.

Example:

URIError

Occurs when an invalid URI is passed to a function. Example: Using an illegal character in a URI function.

Example:

Non-Standard Error Object Properties

Some browsers add additional properties like

fileName

lineNumber

columnNumber

stack

description

number

But these are not standardized. These properties should not be used on public websites. Not every browser will be able to use them.

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JavaScript Errors