# JavaScript Error Objects

> Learn about the JavaScript error objects, Error, RangeError, ReferenceError, SyntaxError and TypeError, their message and name properties, and when each fires.

Author: Flavio Copes | Published: 2019-06-20 | Canonical: https://flaviocopes.com/javascript-errors/

[JavaScript](https://flaviocopes.com/javascript/) gives us 7 *error objects*, which are raised in a try/catch expression depending on the error type:

- `Error`
- `EvalError`
- `RangeError`
- `ReferenceError`
- `SyntaxError`
- `TypeError`
- `URIError`

Let's analyze each one of those.

## Error

This is the generic error, and it's the one all the other error objects inherit from. You will never see an instance of `Error` directly, but rather JavaScript fires one of the other errors listed above, which inherit from `Error`.

It contains 2 properties:

- `message`: the error description, a human readable message that should explain what error happened
- `name`: the type of error occurred (assumes the value of the specific error object name, for example, `TypeError` or `SyntaxError`)

and provides just one method, `toString()`, which is responsible for generating a meaningful string from the error, which can be used to print it to screen.

## EvalError

This error is defined in modern JavaScript but never actually thrown by JavaScript, and remains for compatibility purposes. It was defined in ECMAScript 3 but it's not present in the standard since ECMAScript 5.1.

It was used to indicate that the global function `eval()` was used incorrectly, in a way incompatible with its definition.

## RangeError

A `RangeError` will fire when a numeric value is not in its range of allowed values.

The simplest example is when you set an array length to a negative value:

```js
[].length = -1 //RangeError: Invalid array length
```

or when you set it to a number higher than `4294967295`

```js
[].length = 4294967295 //4294967295
[].length = 4294967296 //RangeError: Invalid array length
```

(this magic number is specified in the JavaScript spec as the maximum range of a 32-bit unsigned integer, equivalent to `Math.pow(2, 32) - 1`)

Here are the most common range errors you can spot in the wild:

- [`RangeError: argument is not a valid code point`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Errors/Not_a_codepoint)
- [`RangeError: invalid array length`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Errors/Invalid_array_length)
- [`RangeError: invalid date`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Errors/Invalid_date)
- [`RangeError: precision is out of range`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Errors/Precision_range)
- [`RangeError: radix must be an integer`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Errors/Bad_radix)
- [`RangeError: repeat count must be less than infinity`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Errors/Resulting_string_too_large)
- [`RangeError: repeat count must be non-negative`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Errors/Negative_repetition_count)

## ReferenceError

A `ReferenceError` indicates that an invalid reference value has been detected: a JavaScript program is trying to read a variable that does not exist.

```js
dog //ReferenceError: dog is not defined
dog = 2 //ReferenceError: dog is not defined
```

Be aware that the above statement will create a `dog` variable on the global object if not ran in **strict mode**.

Here are the most common reference errors you can spot in the wild:

- [`ReferenceError: "x" is not defined`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Errors/Not_defined)
- [`ReferenceError: assignment to undeclared variable "x"`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Errors/Undeclared_var)
- [`ReferenceError: can't access lexical declaration 'X' before initialization`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Errors/Cant_access_lexical_declaration_before_init)
- [`ReferenceError: deprecated caller or arguments usage`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Errors/Deprecated_caller_or_arguments_usage)
- [`ReferenceError: invalid assignment left-hand side`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Errors/Invalid_assignment_left-hand_side)
- [`ReferenceError: reference to undefined property "x"`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Errors/Undefined_prop)

## SyntaxError

A `SyntaxError` is raised when a syntax error is found in a program.

Here are some examples of code that generate a syntax error.

A function statement without name:

```js
function() {
  return 'Hi!'
}
//SyntaxError: function statement requires a name
```

Missing comma after an object property definition:

```js
const dog = {
  name: 'Roger'
  age: 5
}
//SyntaxError: missing } after property list
```

Here are the most common syntax errors you can spot in the wild:

- [`SyntaxError: "0"-prefixed octal literals and octal escape seq. are deprecated`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Errors/Deprecated_octal)
- [`SyntaxError: "use strict" not allowed in function with non-simple parameters`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Errors/Strict_Non_Simple_Params)
- [`SyntaxError: "x" is a reserved identifier`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Errors/Reserved_identifier)
- [`SyntaxError: JSON.parse: bad parsing`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Errors/JSON_bad_parse)
- [`SyntaxError: Malformed formal parameter`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Errors/Malformed_formal_parameter)
- [`SyntaxError: Unexpected token`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Errors/Unexpected_token)
- [`SyntaxError: Using //@ to indicate sourceURL pragmas is deprecated. Use //# instead`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Errors/Deprecated_source_map_pragma)
- [`SyntaxError: a declaration in the head of a for-of loop can't have an initializer`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Errors/Invalid_for-of_initializer)
- [`SyntaxError: applying the 'delete' operator to an unqualified name is deprecated`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Errors/Delete_in_strict_mode)
- [`SyntaxError: for-in loop head declarations may not have initializers`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Errors/Invalid_for-in_initializer)
- [`SyntaxError: function statement requires a name`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Errors/Unnamed_function_statement)
- [`SyntaxError: identifier starts immediately after numeric literal`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Errors/Identifier_after_number)
- [`SyntaxError: illegal character`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Errors/Illegal_character)
- [`SyntaxError: invalid regular expression flag "x"`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Errors/Bad_regexp_flag)
- [`SyntaxError: missing ) after argument list`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Errors/Missing_parenthesis_after_argument_list)
- [`SyntaxError: missing ) after condition`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Errors/Missing_parenthesis_after_condition)
- [`SyntaxError: missing : after property id`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Errors/Missing_colon_after_property_id)
- [`SyntaxError: missing ; before statement`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Errors/Missing_semicolon_before_statement)
- [`SyntaxError: missing = in const declaration`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Errors/Missing_initializer_in_const)
- [`SyntaxError: missing \] after element list`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Errors/Missing_bracket_after_list)
- [`SyntaxError: missing formal parameter`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Errors/Missing_formal_parameter)
- [`SyntaxError: missing name after . operator`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Errors/Missing_name_after_dot_operator)
- [`SyntaxError: missing variable name`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Errors/No_variable_name)
- [`SyntaxError: missing } after function body`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Errors/Missing_curly_after_function_body)
- [`SyntaxError: missing } after property list`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Errors/Missing_curly_after_property_list)
- [`SyntaxError: redeclaration of formal parameter "x"`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Errors/Redeclared_parameter)
- [`SyntaxError: return not in function`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Errors/Bad_return_or_yield)
- [`SyntaxError: test for equality (==) mistyped as assignment (=)?`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Errors/Equal_as_assign)
- [`SyntaxError: unterminated string literal`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Errors/Unterminated_string_literal)

## TypeError

A `TypeError` happens when a value has a type that's different than the one expected.

The simplest example is trying to invoke a number:

```js
1() //TypeError: 1 is not a function
```

Here are the most common type errors you can spot in the wild:

- [`TypeError: "x" has no properties`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Errors/No_properties)
- [`TypeError: "x" is (not) "y"`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Errors/Unexpected_type)
- [`TypeError: "x" is not a constructor`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Errors/Not_a_constructor)
- [`TypeError: "x" is not a function`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Errors/Not_a_function)
- [`TypeError: "x" is not a non-null object`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Errors/No_non-null_object)
- [`TypeError: "x" is read-only`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Errors/Read-only)
- [`TypeError: 'x' is not iterable`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Errors/is_not_iterable)
- [`TypeError: More arguments needed`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Errors/More_arguments_needed)
- [`TypeError: Reduce of empty array with no initial value`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Errors/Reduce_of_empty_array_with_no_initial_value)
- [`TypeError: can't access dead object`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Errors/Dead_object)
- [`TypeError: can't access property "x" of "y"`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Errors/Cant_access_property)
- [`TypeError: can't define property "x": "obj" is not extensible`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Errors/Cant_define_property_object_not_extensible)
- [`TypeError: can't delete non-configurable array element`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Errors/Non_configurable_array_element)
- [`TypeError: can't redefine non-configurable property "x"`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Errors/Cant_redefine_property)
- [`TypeError: cannot use 'in' operator to search for 'x' in 'y'`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Errors/in_operator_no_object)
- [`TypeError: cyclic object value`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Errors/Cyclic_object_value)
- [`TypeError: invalid 'instanceof' operand 'x'`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Errors/invalid_right_hand_side_instanceof_operand)
- [`TypeError: invalid Array.prototype.sort argument`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Errors/Array_sort_argument)
- [`TypeError: invalid arguments`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Errors/Typed_array_invalid_arguments)
- [`TypeError: invalid assignment to const "x"`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Errors/Invalid_const_assignment)
- [`TypeError: property "x" is non-configurable and can't be deleted`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Errors/Cant_delete)
- [`TypeError: setting getter-only property "x"`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Errors/Getter_only)
- [`TypeError: variable "x" redeclares argument`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Errors/Var_hides_argument)

## URIError

This error is raised when calling one of the global functions that work with URIs:

- `decodeURI()`
- `decodeURIComponent()`
- `encodeURI()`
- `encodeURIComponent()`

and passing an invalid URI.