What types of errors exist in JavaScript?

JavaScriptJunior~2 min read

1. `Error` - the base error class

This is the universal type that all other errors inherit from. If you are not sure which error type fits, you can just use Error.

javascript

throw new Error("Something went wrong!");

Properties:

name - the error's name ("Error")
message - the description
stack - the stack trace (shows where the error occurred)

2. `ReferenceError` - a reference error

Occurs when there is a reference to a non-existent variable or a property that is not accessible in the current scope.

javascript

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

It can also occur from incorrect use of this.

3. `TypeError` - a type error

Occurs when an operation is applied to a value of the wrong type, or when something that is not a function is called.

javascript

let n = null;
console.log(n.toString()); // TypeError: Cannot read properties of null

javascript

let func = 123;
func(); // TypeError: func is not a function

4. `RangeError` - out of the allowed range

Occurs when a passed value is outside the allowed range.

javascript

new Array(-5); // RangeError: Invalid array length

javascript

(123.456).toFixed(200); // RangeError: toFixed() digits argument must be between 0 and 100

5. `SyntaxError` - a syntax error

An error caused by violating JavaScript syntax. The engine cannot "parse" the code, so the program does not even start.

javascript

eval("if (true { console.log('hi'); }");
// SyntaxError: Unexpected token '{'

Such errors cannot be caught with try...catch, because they occur before execution even begins.

6. `URIError` - an error in URI functions

Occurs if the encodeURI(), decodeURI(), encodeURIComponent(), or decodeURIComponent() functions receive invalid data.

javascript

decodeURIComponent("%");
// URIError: URI malformed

7. `EvalError` - an error from using `eval()`

Rare in modern implementations. Originally used when eval() was used incorrectly.

javascript

throw new EvalError("Incorrect use of eval()");

8. (Additionally) `AggregateError` - a set of errors

Occurs when a single operation returns several errors at once, for example with Promise.any().

javascript

Promise.any([
  Promise.reject(new Error("Error 1")),
  Promise.reject(new Error("Error 2")),
]).catch(e => console.log(e.errors));

Output:

javascript

[Error: Error 1, Error: Error 2]

9. Custom errors

You can create your own error classes by extending Error:

javascript

class ValidationError extends Error {
  constructor(message) {
    super(message);
    this.name = "ValidationError";
  }
}

throw new ValidationError("Invalid email");

Output:

javascript

ValidationError: Invalid email

Summary table

Error type	When it occurs	Example
Error	The base class for all errors	`throw new Error("Error!")`
ReferenceError	A variable is not defined	`console.log(x)`
TypeError	The value has the wrong type	`null.toString()`
RangeError	A value is outside the allowed range	`new Array(-1)`
SyntaxError	A syntax error	`eval("if (true {")`
URIError	An error encoding/decoding a URI	`decodeURI("%")`
EvalError	An `eval()` error (rarely used)	`throw new EvalError()`
AggregateError	Several errors at once	`Promise.any([...])`

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