JavaScript Guide

The JavaScript Guide shows you how to use JavaScript and gives an overview of the language. If you need exhaustive information about a language feature, have a look at the JavaScript reference.

Chapters

This Guide is divided into several chapters:

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Related Topics
  1. JavaScript
  2. Tutorials:
  3. Complete beginners
    1. JavaScript basics
    2. JavaScript first steps
    3. JavaScript building blocks
    4. Introducing JavaScript objects
  4. JavaScript Guide
    1. Introduction
    2. Grammar and types
    3. Control flow and error handling
    4. Loops and iteration
    5. Functions
    6. Expressions and operators
    7. Numbers and dates
    8. Text formatting
    9. Regular expressions
    10. Indexed collections
    11. Keyed collections
    12. Working with objects
    13. Details of the object model
    14. Using promises
    15. Iterators and generators
    16. Meta programming
    17. JavaScript modules
  5. Intermediate
    1. Introducing JavaScript objects
    2. Client-side web APIs
    3. A re-introduction to JavaScript
    4. JavaScript data structures
    5. Equality comparisons and sameness
    6. Closures
  6. Advanced
    1. Inheritance and the prototype chain
    2. Strict mode
    3. JavaScript typed arrays
    4. Memory Management
    5. Concurrency model and Event Loop
  7. References:
  8. Built-in objects
    1. Array
    2. ArrayBuffer
    3. AsyncFunction
    4. Atomics
    5. BigInt
    6. BigInt64Array
    7. BigUint64Array
    8. Boolean
    9. DataView
    10. Date
    11. Error
    12. EvalError
    13. Float32Array
    14. Float64Array
    15. Function
    16. Generator
    17. GeneratorFunction
    18. Infinity
    19. Int16Array
    20. Int32Array
    21. Int8Array
    22. InternalError
    23. Intl
    24. Intl.Collator
    25. Intl.DateTimeFormat
    26. Intl.ListFormat
    27. Intl.Locale
    28. Intl.NumberFormat
    29. Intl.PluralRules
    30. Intl.RelativeTimeFormat
    31. JSON
    32. Map
    33. Math
    34. NaN
    35. Number
    36. Object
    37. Promise
    38. Proxy
    39. RangeError
    40. ReferenceError
    41. Reflect
    42. RegExp
    43. Set
    44. SharedArrayBuffer
    45. String
    46. Symbol
    47. SyntaxError
    48. TypeError
    49. TypedArray
    50. URIError
    51. Uint16Array
    52. Uint32Array
    53. Uint8Array
    54. Uint8ClampedArray
    55. WeakMap
    56. WeakSet
    57. WebAssembly
    58. decodeURI()
    59. decodeURIComponent()
    60. encodeURI()
    61. encodeURIComponent()
    62. escape()
    63. eval()
    64. globalThis
    65. isFinite()
    66. isNaN()
    67. null
    68. parseFloat()
    69. parseInt()
    70. undefined
    71. unescape()
    72. uneval()
  9. Expressions & operators
    1. Arithmetic operators
    2. Array comprehensions
    3. Assignment operators
    4. Bitwise operators
    5. Comma operator
    6. Comparison operators
    7. Conditional (ternary) operator
    8. Destructuring assignment
    9. Expression closures
    10. Generator comprehensions
    11. Grouping operator
    12. Legacy generator function expression
    13. Logical operators
    14. Object initializer
    15. Operator precedence
    16. Optional chaining
    17. Pipeline operator
    18. Property accessors
    19. Spread syntax
    20. async function expression
    21. await
    22. class expression
    23. delete operator
    24. function expression
    25. function* expression
    26. in operator
    27. instanceof
    28. new operator
    29. new.target
    30. super
    31. this
    32. typeof
    33. void operator
    34. yield
    35. yield*
  10. Statements & declarations
    1. Legacy generator function
    2. async function
    3. block
    4. break
    5. class
    6. const
    7. continue
    8. debugger
    9. default
    10. do...while
    11. empty
    12. export
    13. for
    14. for await...of
    15. for each...in
    16. for...in
    17. for...of
    18. function declaration
    19. function*
    20. if...else
    21. import
    22. import.meta
    23. label
    24. let
    25. return
    26. switch
    27. throw
    28. try...catch
    29. var
    30. while
    31. with
  11. Functions
    1. Arrow function expressions
    2. Default parameters
    3. Method definitions
    4. Rest parameters
    5. The arguments object
    6. getter
    7. setter
  12. Classes
    1. Class fields
    2. constructor
    3. extends
    4. static
  13. Errors
    1. Error: Permission denied to access property "x"
    2. InternalError: too much recursion
    3. RangeError: argument is not a valid code point
    4. RangeError: invalid array length
    5. RangeError: invalid date
    6. RangeError: precision is out of range
    7. RangeError: radix must be an integer
    8. RangeError: repeat count must be less than infinity
    9. RangeError: repeat count must be non-negative
    10. ReferenceError: "x" is not defined
    11. ReferenceError: assignment to undeclared variable "x"
    12. ReferenceError: can't access lexical declaration`X' before initialization
    13. ReferenceError: deprecated caller or arguments usage
    14. ReferenceError: invalid assignment left-hand side
    15. ReferenceError: reference to undefined property "x"
    16. SyntaxError: "0"-prefixed octal literals and octal escape seq. are deprecated
    17. SyntaxError: "use strict" not allowed in function with non-simple parameters
    18. SyntaxError: "x" is a reserved identifier
    19. SyntaxError: JSON.parse: bad parsing
    20. SyntaxError: Malformed formal parameter
    21. SyntaxError: Unexpected token
    22. SyntaxError: Using //@ to indicate sourceURL pragmas is deprecated. Use //# instead
    23. SyntaxError: a declaration in the head of a for-of loop can't have an initializer
    24. SyntaxError: applying the 'delete' operator to an unqualified name is deprecated
    25. SyntaxError: for-in loop head declarations may not have initializers
    26. SyntaxError: function statement requires a name
    27. SyntaxError: identifier starts immediately after numeric literal
    28. SyntaxError: illegal character
    29. SyntaxError: invalid regular expression flag "x"
    30. SyntaxError: missing ) after argument list
    31. SyntaxError: missing ) after condition
    32. SyntaxError: missing : after property id
    33. SyntaxError: missing ; before statement
    34. SyntaxError: missing = in const declaration
    35. SyntaxError: missing ] after element list
    36. SyntaxError: missing formal parameter
    37. SyntaxError: missing name after . operator
    38. SyntaxError: missing variable name
    39. SyntaxError: missing } after function body
    40. SyntaxError: missing } after property list
    41. SyntaxError: redeclaration of formal parameter "x"
    42. SyntaxError: return not in function
    43. SyntaxError: test for equality (==) mistyped as assignment (=)?
    44. SyntaxError: unterminated string literal
    45. TypeError: "x" has no properties
    46. TypeError: "x" is (not) "y"
    47. TypeError: "x" is not a constructor
    48. TypeError: "x" is not a function
    49. TypeError: "x" is not a non-null object
    50. TypeError: "x" is read-only
    51. TypeError: 'x' is not iterable
    52. TypeError: More arguments needed
    53. TypeError: Reduce of empty array with no initial value
    54. TypeError: X.prototype.y called on incompatible type
    55. TypeError: can't access dead object
    56. TypeError: can't access property "x" of "y"
    57. TypeError: can't assign to property "x" on "y": not an object
    58. TypeError: can't define property "x": "obj" is not extensible
    59. TypeError: can't delete non-configurable array element
    60. TypeError: can't redefine non-configurable property "x"
    61. TypeError: cannot use 'in' operator to search for 'x' in 'y'
    62. TypeError: cyclic object value
    63. TypeError: invalid 'instanceof' operand 'x'
    64. TypeError: invalid Array.prototype.sort argument
    65. TypeError: invalid arguments
    66. TypeError: invalid assignment to const "x"
    67. TypeError: property "x" is non-configurable and can't be deleted
    68. TypeError: setting getter-only property "x"
    69. TypeError: variable "x" redeclares argument
    70. URIError: malformed URI sequence
    71. Warning: -file- is being assigned a //# sourceMappingURL, but already has one
    72. Warning: 08/09 is not a legal ECMA-262 octal constant
    73. Warning: Date.prototype.toLocaleFormat is deprecated
    74. Warning: JavaScript 1.6's for-each-in loops are deprecated
    75. Warning: String.x is deprecated; use String.prototype.x instead
    76. Warning: expression closures are deprecated
    77. Warning: unreachable code after return statement
  14. Misc
    1. JavaScript technologies overview
    2. Lexical grammar
    3. JavaScript data structures
    4. Enumerability and ownership of properties
    5. Iteration protocols
    6. Strict mode
    7. Transitioning to strict mode
    8. Template literals
    9. Deprecated features
  15. New in JavaScript
    1. ECMAScript 2015 support in Mozilla
    2. ECMAScript 5 support in Mozilla
    3. Firefox JavaScript changelog
    4. New in JavaScript 1.1
    5. New in JavaScript 1.2
    6. New in JavaScript 1.3
    7. New in JavaScript 1.4
    8. New in JavaScript 1.5
    9. New in JavaScript 1.6
    10. New in JavaScript 1.7
    11. New in JavaScript 1.8
    12. New in JavaScript 1.8.1
    13. New in JavaScript 1.8.5
  16. Documentation:
  17. Useful lists
    1. All pages index
    2. Methods index
    3. Properties index
    4. Pages tagged "JavaScript"
  18. Contribute
    1. JavaScript doc status
    2. The MDN project