关于 JavaScript

What is JavaScript?

JavaScript ® (often shortened to JS ) is a lightweight, interpreted, object-oriented language with 一类函数 , and is best known as the scripting language for Web pages, but it's used in many non-browser environments as well. It is a 基于原型 , multi-paradigm scripting language that is dynamic, and supports object-oriented, imperative, and functional programming styles.

JavaScript runs on the client side of the web, which can be used to design / program how the web pages behave on the occurrence of an event. JavaScript is an easy to learn and also powerful scripting language, widely used for controlling web page behavior.

Contrary to popular misconception, JavaScript is not "Interpreted Java" . In a nutshell, JavaScript is a dynamic scripting language supporting prototype based object construction. The basic syntax is intentionally similar to both Java and C++ to reduce the number of new concepts required to learn the language. Language constructs, such as if statements, for and while loops, and switch and try ... catch blocks function the same as in these languages (or nearly so).

JavaScript can function as both a procedural object oriented language . Objects are created programmatically in JavaScript, by attaching methods and properties to otherwise empty objects at run time , as opposed to the syntactic class definitions common in compiled languages like C++ and Java. Once an object has been constructed it can be used as a blueprint (or prototype) for creating similar objects.

JavaScript's dynamic capabilities include runtime object construction, variable parameter lists, function variables, dynamic script creation (via eval ), object introspection (via for ... in ), and source code recovery (JavaScript programs can decompile function bodies back into their source text).

For a more in depth discussion of JavaScript programming follow the JavaScript resources links below.

What JavaScript implementations are available?

The Mozilla project provides two JavaScript implementations. The first ever JavaScript was created by Brendan Eich at Netscape, and has since been updated to conform to ECMA-262 Edition 5 and later versions. This engine, code named SpiderMonkey , is implemented in C/C++. The Rhino engine, created primarily by Norris Boyd (also at Netscape) is a JavaScript implementation written in Java. Like SpiderMonkey, Rhino is ECMA-262 Edition 5 compliant.

Several major runtime optimizations such as TraceMonkey (Firefox 3.5), JägerMonkey (Firefox 4) and IonMonkey were added to the SpiderMonkey JavaScript engine over time. Work is always ongoing to improve JavaScript execution performance.

Besides the above implementations, there are other popular JavaScript engines such as:-

  • Google's V8 , which is used in the Google Chrome browser and recent versions of Opera browser. This is also the engine used by Node.js .
  • JavaScriptCore (SquirrelFish/Nitro) used in some WebKit browsers such as Apple Safari.
  • Carakan in old versions of Opera.
  • Chakra engine used in Internet Explorer (although the language it implements is formally called "JScript" in order to avoid trademark issues).

Each of Mozilla's JavaScript engines expose a public API which application developers can use to integrate JavaScript into their software. By far, the most common host environment for JavaScript is web browsers. Web browsers typically use the public API to create host objects responsible for reflecting the DOM into JavaScript.

Another common application for JavaScript is as a (Web) server side scripting language. A JavaScript web server would expose host objects representing a HTTP request and response objects, which could then be manipulated by a JavaScript program to dynamically generate web pages. Node.js is a popular example of this.

JavaScript resources

SpiderMonkey
Information specific to Mozilla's implementation of JavaScript in C/C++ engine (aka SpiderMonkey), including how to embed it in applications.
Rhino
Information specific to the JavaScript implementation written in Java (aka Rhino).
Language resources
Pointers to published JavaScript standards.
重新介绍 JavaScript
JavaScript 指南 and JavaScript 参考 .

JavaScript® is a trademark or registered trademark of Oracle in the U.S. and other countries.

  1. JavaScript
  2. 教程:
  3. 完整初学者
    1. JavaScript 基础
    2. JavaScript 第一步
    3. JavaScript 构建块
    4. 引入 JavaScript 对象
  4. JavaScript 指南
    1. 介绍
    2. 语法和类型
    3. 控制流程和错误处理
    4. 循环和迭代
    5. 函数
    6. 表达式和运算符
    7. 数字和日期
    8. 文本格式
    9. 正则表达式
    10. Indexed collections
    11. Keyed collections
    12. Working with objects
    13. 对象模型的细节
    14. Using promises
    15. 迭代器和生成器
    16. Meta programming
    17. JavaScript 模块
  5. 中间体
    1. 引入 JavaScript 对象
    2. 客户端侧 Web API
    3. 重新介绍 JavaScript
    4. JavaScript 数据结构
    5. 相等比较和相同
    6. 闭包
  6. 高级
    1. 继承和原型链
    2. 严格模式
    3. JavaScript 类型数组
    4. 内存管理
    5. 并发模型和事件循环
  7. 参考:
  8. 内置对象
    1. AggregateError
    2. Array
    3. ArrayBuffer
    4. AsyncFunction
    5. AsyncIterator
    6. Atomics
    7. BigInt
    8. BigInt64Array
    9. BigUint64Array
    10. Boolean
    11. DataView
    12. Date
    13. Error
    14. EvalError
    15. Float32Array
    16. Float64Array
    17. Function
    18. Generator
    19. GeneratorFunction
    20. Infinity
    21. Int16Array
    22. Int32Array
    23. Int8Array
    24. InternalError
    25. Intl
    26. Intl.Collator
    27. Intl.DateTimeFormat
    28. Intl.DisplayNames
    29. Intl.ListFormat
    30. Intl.Locale
    31. Intl.NumberFormat
    32. Intl.PluralRules
    33. Intl.RelativeTimeFormat
    34. Iterator
    35. JSON
    36. Map
    37. Math
    38. NaN
    39. Number
    40. Object
    41. Promise
    42. Proxy
    43. RangeError
    44. ReferenceError
    45. Reflect
    46. RegExp
    47. Set
    48. SharedArrayBuffer
    49. String
    50. Symbol
    51. SyntaxError
    52. TypeError
    53. TypedArray
    54. URIError
    55. Uint16Array
    56. Uint32Array
    57. Uint8Array
    58. Uint8ClampedArray
    59. WeakMap
    60. WeakSet
    61. WebAssembly
    62. decodeURI()
    63. decodeURIComponent()
    64. encodeURI()
    65. encodeURIComponent()
    66. escape()
    67. eval()
    68. globalThis
    69. isFinite()
    70. isNaN()
    71. null
    72. parseFloat()
    73. parseInt()
    74. undefined
    75. unescape()
    76. uneval()
  9. 表达式 & 运算符
    1. 算术运算符
    2. Array comprehensions
    3. 赋值运算符
    4. Bitwise operators
    5. 逗号运算符
    6. Comparison operators
    7. 条件 (三元) 运算符
    8. Destructuring assignment
    9. Expression closures
    10. Function expression
    11. Generator comprehensions
    12. Grouping operator
    13. Legacy generator function expression
    14. Logical operators
    15. Nullish coalescing operator
    16. Object initializer
    17. 运算符优先级
    18. Optional chaining
    19. Pipeline operator
    20. 特性访问器
    21. 传播句法
    22. 异步函数表达式
    23. await
    24. class expression
    25. delete operator
    26. function* 表达式
    27. in operator
    28. instanceof
    29. new operator
    30. new.target
    31. super
    32. this
    33. typeof
    34. void 运算符
    35. yield
    36. yield*
  10. 语句 & 声明
    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. 函数声明
    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. 函数
    1. 箭头函数表达式
    2. 默认参数
    3. 方法定义
    4. 其余参数
    5. 自变量对象
    6. getter
    7. setter
    1. Class fields
    2. 构造函数
    3. extends
    4. static
  12. 错误
    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
  13. 杂项
    1. JavaScript technologies overview
    2. 词汇语法
    3. JavaScript 数据结构
    4. Enumerability and ownership of properties
    5. Iteration protocols
    6. 严格模式
    7. Transitioning to strict mode
    8. Template literals
    9. 弃用特征