What is an error in JavaScript?

JavaScriptJunior~1 min read

An error in JavaScript is an object that represents a problem that occurred while the program was running. When JavaScript hits a situation it cannot handle (for example, dividing by zero, referencing a nonexistent variable, invalid syntax, and so on), it creates an error object and "throws" it. If the error is not "caught", code execution stops.

The basic idea

Errors exist to control unforeseen situations - so the program does not "crash" unexpectedly, but can handle the problem and keep running correctly.

Example of an error occurring

javascript

console.log(a); // ReferenceError: a is not defined

Here the variable a is not declared, so the interpreter creates and throws a ReferenceError.

Handling errors (try...catch)

So the program does not stop, errors can be handled with a try...catch construct:

javascript

try {
  let result = JSON.parse("invalid JSON");
} catch (error) {
  console.log("An error occurred:", error.message);
}

In this example the program does not crash, it simply prints a message:

javascript

An error occurred: Unexpected token i in JSON at position 0

Main error types

Error type	When it occurs
ReferenceError	Referencing a nonexistent variable
TypeError	Wrong data type (for example, calling something that is not a function)
SyntaxError	An error in the code's syntax
RangeError	A value out of its allowed range
EvalError	Incorrect use of `eval()`
URIError	An error while working with URI-encoding functions (`decodeURI`, `encodeURI`)

Creating your own errors

You can create and throw an error yourself with throw:

javascript

function divide(a, b) {
  if (b === 0) {
    throw new Error("Cannot divide by zero!");
  }
  return a / b;
}

try {
  divide(5, 0);
} catch (err) {
  console.log(err.message); // Cannot divide by zero!
}

Key methods and properties of the Error object

Property	Description
`name`	The error type's name (`TypeError`, `ReferenceError`, etc.)
`message`	The error description
`stack`	The stack trace (shows where the error occurred)

Short Answer

Interview ready

Premium

A concise answer to help you respond confidently on this topic during an interview.

What is an error in JavaScript?

#The basic idea

#Example of an error occurring

#Handling errors (try...catch)

#Main error types

#Creating your own errors

#Key methods and properties of the Error object

Short Answer

The basic idea

Example of an error occurring

Handling errors (try...catch)

Main error types

Creating your own errors

Key methods and properties of the Error object