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ECMAScript Edition 4 Draft是为定义ECMAScript第四版脚本语言标准而制定的草案。ECMAScript是一种广泛应用于网络浏览器脚本编程的语言，由ECMA国际标准化组织维护。ECMAScript Edition 4 Draft旨在扩展和改进该语言，为其提供更强大的功能和更高级的编程抽象。文档内容涵盖了一系列编程概念和技术规范，从基本的文本格式、语义域到复杂的语法和语义动作都有涉及。具体知识点涵盖了： 1. 文档结构与规范：ECMAScript Edition 4 Draft遵循一定的格式和结构，包括文档的范围、一致性要求、标准化参考文献、概述、符号约定等。这些内容为理解整个标准提供了基础框架和背景信息。 2. 符号约定和注释：标准中使用不同颜色的文本以保持字符样式的统一性，有助于开发者快速识别代码的不同部分。这种做法虽然在最终草案中会被移除，但在开发和审阅过程中非常有帮助。 3. 数值类型：ECMAScript Edition 4 Draft介绍了多种数值类型，包括有符号和无符号长整数、单精度和双精度浮点数，并提供了它们的简写表示法、转换规则和算术运算规则。 4. 数据模型：标准定义了ECMAScript中的数据模型，包括对象的定义、数据类型（如Undefined、Null、Booleans、Numbers、Strings、Namespaces等）、类和简单实例、未实例化的函数、方法闭包、日期、正则表达式以及包和全局对象。此外，还提到了具有限制的对象。 5. 语法结构：标准描述了ECMAScript的语法结构，包括输入元素、空白字符、换行、注释、关键字和标识符、标点符号、数值字面量、字符串字面量、正则表达式字面量等。 6. 程序结构：文档阐述了ECMAScript程序的结构，比如包的概念和作用域规则。 7. 操作和语义动作：草案详细说明了操作的类型、程序的语义域、步骤、嵌套程序等，并提供了语义动作的详细描述和示例。 8. 正则表达式：标准中提到了正则表达式的语法和语义，这是ECMAScript支持模式匹配功能的基础。 9. Unicode和控制字符：文档规定了源文本的Unicode格式和控制字符的使用。 10. 语法：文档详细说明了ECMAScript的语法记法、前瞻约束、行断点约束、参数化规则以及特殊的词法规则。 ECMAScript Edition 4 Draft的制定，意味着该语言未来版本将带来大量的新特性，这将为开发者提供更强大的工具集，同时也会对现有的基于ECMAScript的编程方式带来影响。开发者需要关注新标准的进展，以便在新版本推出时，能快速适应并充分利用其新功能。然而，需要注意的是，ECMAScript第四版并未正式成为标准，因此其内容可能会有变动。最终ECMAScript第四版的特性也可能会因为社区和开发者反馈而有所调整，而ECMAScript的最新标准可以通过ECMA TC39委员会的工作和ECMAScript的发布年历来查找。

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ECMAScript Edition 4 Draft 3/24/03 8:43 PM 1

NOTE: I am using colours in this document to ensure that character styles are applied consistently. They can be removed by

changing Word’s character styles and will be removed for the final draft.

Table of Contents

1 Scope .....................................................................................3

2 Conformance .........................................................................3

3 Normative References...........................................................3

4 Overview ...............................................................................3

5 Notational Conventions ........................................................3

5.1 Text.................................................................................3

5.2 Semantic Domains .........................................................3

5.3 Tags ................................................................................4

5.4 Booleans.........................................................................4

5.5 Sets .................................................................................4

5.6 Real Numbers.................................................................6

5.6.1 Bitwise Integer Operators.......................................6

5.7 Characters.......................................................................7

5.8 Lists ................................................................................7

5.9 Strings.............................................................................8

5.10 Tuples...........................................................................9

5.10.1 Shorthand Notation...............................................9

5.11 Records.........................................................................9

5.12 ECMAScript Numeric Types ....................................10

5.12.1 Signed Long Integers..........................................10

5.12.1.1 Shorthand Notation .....................................10

5.12.2 Unsigned Long Integers .....................................10

5.12.2.1 Shorthand Notation .....................................11

5.12.3 Single-Precision Floating-Point Numbers .........11

5.12.3.1 Shorthand Notation .....................................11

5.12.3.2 Conversion...................................................11

5.12.3.3 Arithmetic....................................................12

5.12.4 Double-Precision Floating-Point Numbers .......12

5.12.4.1 Shorthand Notation .....................................13

5.12.4.2 Conversion...................................................13

5.12.4.3 Arithmetic....................................................14

5.13 Procedures..................................................................15

5.13.1 Operations...........................................................16

5.13.2 Semantic Domains of Procedures ......................16

5.13.3 Steps ....................................................................16

5.13.4 Nested Procedures ..............................................18

5.14 Grammars...................................................................18

5.14.1 Grammar Notation..............................................18

5.14.2 Lookahead Constraints .......................................19

5.14.3 Line Break Constraints.......................................19

5.14.4 Parameterised Rules ...........................................19

5.14.5 Special Lexical Rules .........................................20

5.15 Semantic Actions .......................................................20

5.15.1 Example ..............................................................21

5.15.2 Abbreviated Actions...........................................22

5.15.3 Action Notation Summary .................................23

5.16 Other Semantic Definitions .......................................24

6 Source Text..........................................................................25

6.1 Unicode Format-Control Characters...........................25

7 Lexical Grammar ................................................................25

7.1 Input Elements .............................................................27

7.2 White space ..................................................................28

7.3 Line Breaks ..................................................................28

7.4 Comments.....................................................................29

7.5 Keywords and Identifiers.............................................29

7.6 Punctuators ...................................................................32

7.7 Numeric literals............................................................32

7.8 String literals ................................................................35

7.9 Regular expression literals...........................................36

8 Program Structure................................................................37

8.1 Packages .......................................................................37

8.2 Scopes...........................................................................37

9 Data Model ..........................................................................37

9.1 Objects..........................................................................37

9.1.1 Undefined..............................................................38

9.1.2 Null........................................................................38

9.1.3 Booleans................................................................38

9.1.4 Numbers ................................................................38

9.1.5 Strings....................................................................38

9.1.6 Namespaces...........................................................39

9.1.6.1 Qualified Names ............................................39

9.1.7 Compound attributes.............................................39

9.1.8 Classes...................................................................40

9.1.9 Simple Instances ...................................................41

9.1.9.1 Slots................................................................41

9.1.10 Uninstantiated Functions ....................................42

9.1.11 Method Closures .................................................42

9.1.12 Dates....................................................................42

9.1.13 Regular Expressions ...........................................42

9.1.14 Packages and Global Objects .............................43

9.2 Objects with Limits......................................................43

9.3 References ....................................................................43

9.4 Function Support..........................................................44

9.5 Phases of evaluation.....................................................44

9.6 Contexts........................................................................44

9.7 Labels ...........................................................................45

9.8 Environment Frames....................................................45

9.8.1 System Frame........................................................46

9.8.2 Function Parameter Frames..................................46

9.8.2.1 Parameters......................................................46

9.8.3 Local Frames.........................................................46

9.9 Environment Bindings .................................................46

9.9.1 Static Bindings ......................................................47

9.9.2 Instance Bindings..................................................48

10 Data Operations.................................................................50

10.1 Numeric Utilities........................................................50

10.2 Object Utilities ...........................................................52

10.2.1 objectType ...........................................................52

10.2.2 toBoolean ............................................................52

10.2.3 toGeneralNumber ...............................................53

2 3/24/03 8:43 PM ECMAScript Edition 4 Draft

10.2.4 toString................................................................53

10.2.5 toQualifiedName.................................................55

10.2.6 toPrimitive ..........................................................55

10.2.7 toClass.................................................................55

10.2.8 Attributes.............................................................56

10.3 Access Utilities ..........................................................56

10.4 Environmental Utilities..............................................57

10.5 Property Lookup ........................................................58

10.6 Reading ......................................................................60

10.7 Writing .......................................................................63

10.8 Deleting ......................................................................67

10.9 Enumerating...............................................................69

10.10 Creating Instances....................................................69

10.11 Adding Local Definitions........................................70

10.12 Adding Instance Definitions....................................71

10.13 Instantiation..............................................................73

11 Evaluation..........................................................................75

11.1 Phases of Evaluation..................................................75

11.2 Constant Expressions.................................................75

12 Expressions........................................................................75

12.1 Identifiers ...................................................................76

12.2 Qualified Identifiers...................................................76

12.3 Primary Expressions ..................................................78

12.4 Function Expressions.................................................80

12.5 Object Literals............................................................81

12.6 Array Literals .............................................................83

12.7 Super Expressions......................................................84

12.8 Postfix Expressions....................................................85

12.9 Member Operators .....................................................90

12.10 Unary Operators.......................................................92

12.11 Multiplicative Operators..........................................94

12.12 Additive Operators...................................................96

12.13 Bitwise Shift Operators ...........................................97

12.14 Relational Operators ................................................99

12.15 Equality Operators.................................................101

12.16 Binary Bitwise Operators ......................................103

12.17 Binary Logical Operators ......................................105

12.18 Conditional Operator .............................................106

12.19 Assignment Operators ...........................................107

12.20 Comma Expressions ..............................................110

12.21 Type Expressions...................................................110

13 Statements .......................................................................111

13.1 Empty Statement......................................................114

13.2 Expression Statement...............................................114

13.3 Super Statement .......................................................115

13.4 Block Statement.......................................................115

13.5 Labeled Statements..................................................116

13.6 If Statement..............................................................117

13.7 Switch Statement .....................................................118

13.8 Do-While Statement ................................................121

13.9 While Statement.......................................................122

13.10 For Statements .......................................................123

13.11 With Statement ......................................................128

13.12 Continue and Break Statements ............................128

13.13 Return Statement....................................................129

13.14 Throw Statement....................................................130

13.15 Try Statement.........................................................130

14 Directives.........................................................................133

14.1 Attributes................................................................. 136

14.2 Use Directive........................................................... 138

14.3 Import Directive...................................................... 139

14.4 Pragma..................................................................... 139

15 Definitions ...................................................................... 141

15.1 Export Definition .................................................... 141

15.2 Variable Definition ................................................. 141

15.3 Simple Variable Definition..................................... 146

15.4 Function Definition................................................. 147

15.5 Class Definition....................................................... 157

15.6 Namespace Definition............................................. 159

15.7 Package Definition.................................................. 159

16 Programs......................................................................... 160

17 Predefined Identifiers..................................................... 161

18 Built-in Classes............................................................... 161

18.1 Object ...................................................................... 165

18.2 Never ....................................................................... 165

18.3 Void ......................................................................... 165

18.4 Null .......................................................................... 165

18.5 Boolean.................................................................... 165

18.6 Integer...................................................................... 165

18.7 Number.................................................................... 165

18.7.1 ToNumber Grammar ....................................... 165

18.8 Character ................................................................. 165

18.9 String ....................................................................... 165

18.10 Function................................................................. 165

18.11 Array...................................................................... 165

18.12 Type....................................................................... 165

18.13 Math....................................................................... 165

18.14 Date........................................................................ 165

18.15 RegExp .................................................................. 165

18.15.1 Regular Expression Grammar ....................... 165

18.16 Error....................................................................... 165

18.17 Attribute ................................................................ 165

19 Built-in Functions........................................................... 165

20 Built-in Attributes .......................................................... 165

21 Built-in Namespaces ...................................................... 166

22 Errors .............................................................................. 166

23 Optional Packages.......................................................... 166

23.1 Machine Types........................................................ 166

23.2 Internationalisation ................................................. 166

A Index ................................................................................ 166

A.1 Nonterminals ............................................................ 166

A.2 Tags........................................................................... 167

A.3 Semantic Domains ................................................... 167

A.4 Globals...................................................................... 168

ECMAScript Edition 4 Draft 3/24/03 8:43 PM 3

1 Scope

This Standard defines the ECMAScript Edition 4 scripting language.

2 Conformance

3 Normative References

4 Overview

5 Notational Conventions

This specification uses the notation below to represent algorithms and concepts. These concepts are used as notation only and

are not necessarily represented or visible in the ECMAScript language.

5.1 Text

Throughout this document, the phrase code point and the word character is used to refer to a 16-bit unsigned value used to

represent a single 16-bit unit of Unicode text in the UTF-16 transformation format. The phrase Unicode character is used to

refer to the abstract linguistic or typographical unit represented by a single Unicode scalar value (which may be longer than

16 bits and thus may be represented by more than one code point). This only refers to entities represented by single Unicode

scalar values: the components of a combining character sequence are still individual Unicode characters, even though a user

might think of the whole sequence as a single character.

When denoted in this specification, characters with values between 20 and 7E hexadecimal inclusive are in a fixed width

font. Other characters are denoted by enclosing their four-digit hexadecimal Unicode value between «u and ». For example,

the non-breakable space character would be denoted in this document as «u00A0». A few of the common control characters

are represented by name:

Abbreviation

Unicode Value

«NUL»

«u0000»

«BS»

«u0008»

«TAB»

«u0009»

«LF»

«u000A»

«VT»

«u000B»

«FF»

«u000C»

«CR»

«u000D»

«SP»

«u0020»

A space character is denoted in this document either by a blank space where it’s obvious from the context or by «SP» where

the space might be confused with some other notation.

5.2 Semantic Domains

Semantic domains describe the possible values that a variable might take on in an algorithm. The algorithms are constructed

in a way that ensures that these constraints are always met, regardless of any valid or invalid programmer or user input or

actions.

4 3/24/03 8:43 PM ECMAScript Edition 4 Draft

A semantic domain can be intuitively thought of as a set of possible values, and, in fact, any set of values explicitly described

in this document is also a semantic domain. Nevertheless, semantic domains have a more precise mathematical definition in

domain theory (see for example David Schmidt, Denotational Semantics: A Methodology for Language Development; Allyn

and Bacon 1986) that allows one to define semantic domains recursively without encountering paradoxes such as trying to

define a set A whose members include all functions mapping values from A to INTEGER. The problem with an ordinary

definition of such a set A is that the cardinality of the set of all functions mapping A to INTEGER is always strictly greater than

the cardinality of A, leading to a contradiction. Domain theory uses a least fixed point construction to allow A to be defined as

a semantic domain without encountering problems.

Semantic domains have names in CAPITALISED SMALL CAPS. Such a name is to be considered distinct from a tag or regular

variable with the same name, so UNDEFINED, undefined, and undefined are three different and independent entities.

A variable v is constrained using the notation

v: T

where T is a semantic domain. This constraint indicates that the value of v will always be a member of the semantic domain

T. These declarations are informative (they may be dropped without affecting the semantics’ correctness) but useful in

understanding the semantics. For example, when the semantics state that x: INTEGER then one does not have to worry about

what happens when x has the value true or +∞.

The constraints can be proven statically. The semantics have been machine-checked to ensure that every constraint holds.

5.3 Tags

Tags are computational tokens with no internal structure. Tags are written using a bold sans-serif font. Two tags are equal

if and only if they have the same name. Examples of tags include true, false, null, NaN, and identifier.

5.4 Booleans

The tags true and false represent Booleans. BOOLEAN is the two-element semantic domain {true, false}.

Let a and b be Booleans. In addition to = and ≠, the following operations can be done on them:

not a

true if a is false; false if a is true

a and b

If a is false, returns false without computing b; if a is true, returns the value of b

a or b

If a is false, returns the value of b; if a is true, returns true without computing b

a xor b

true if a is true and b is false or a is false and b is true; false otherwise. a xor b is equivalent to a ≠ b

Note that the and and or operators short-circuit. These are the only operators that do not always compute all of their

operands.

5.5 Sets

A set is an unordered, possibly infinite collection of elements. Each element may occur at most once in a set. There must be

an equivalence relation = defined on all pairs of the set’s elements. Elements of a set may themselves be sets.

A set is denoted by enclosing a comma-separated list of values inside braces:

{element

, element

, ... , element

}

The empty set is written as {}. Any duplicate elements are included only once in the set.

For example, the set {3, 0, 10, 11, 12, 13, -5} contains seven integers.

Sets of either integers or characters can be abbreviated using the ... range operator. For example, the above set can also be

written as {0, –5, 3 ... 3, 10 ... 13}.

ECMAScript Edition 4 Draft 3/24/03 8:43 PM 5

If the beginning of the range is equal to the end of the range, then the range consists of only one element: {7 ... 7} is the same

as {7}. If the end of the range is one less than the beginning, then the range contains no elements: {7 ... 6} is the same as {}.

The end of the range is never more than one less than the beginning.

A set can also be written using the set comprehension notation

{f(x) | "x Œ A}

which denotes the set of the results of computing expression f on all elements x of set A. A predicate can be added:

{f(x) | "x Œ A such that predicate(x)}

denotes the set of the results of computing expression f on all elements x of set A that satisfy the predicate expression. There

can also be more than one free variable x and set A, in which case all combinations of free variables’ values are considered.

For example,

{x | "x Œ INTEGER such that x

< 10} = {–3, –2, –1, 0, 1, 2, 3}

| "x Œ {–5, –1, 1, 2, 4}} = {1, 4, 16, 25}

{x¥10 + y | "x Œ {1, 2, 4}, "y Œ {3, 5}} = {13, 15, 23, 25, 43, 45}

The same notation is used for operations on sets and on semantic domains. Let A and B be sets (or semantic domains) and x

and y be values. The following operations can be done on them:

x Œ A

true if x is an element of A and false if not

x œ A

false if x is an element of A and true if not

|A|

The number of elements in A (only used on finite sets)

min A

The value m that satisfies both m Œ A and for all elements x Œ A, x ≥ m (only used on nonempty, finite sets whose

elements have a well-defined order relation)

max A

The value m that satisfies both m Œ A and for all elements x Œ A, x ≤ m (only used on nonempty, finite sets whose

elements have a well-defined order relation)

A « B

The intersection of A and B (the set or semantic domain of all values that are present both in A and in B)

A » B

The union of A and B (the set or semantic domain of all values that are present in at least one of A or B)

A – B

The difference of A and B (the set or semantic domain of all values that are present in A but not B)

A = B

true if A and B are equal and false otherwise. A and B are equal if every element of A is also in B and every

element of B is also in A.

A ≠ B

false if A and B are equal and true otherwise

A Õ B

true if A is a subset of B and false otherwise. A is a subset of B if every element of A is also in B. Every set is a

subset of itself. The empty set {} is a subset of every set.

A Ã B

true if A is a proper subset of B and false otherwise. A Ã B is equivalent to A Õ B and A ≠ B.

If T is a semantic domain, then T{} is the semantic domain of all sets whose elements are members of T. For example, if

T = {1,2,3}

then:

T{} = {{}, {1}, {2}, {3}, {1,2}, {1,3}, {2,3}, {1,2,3}}

The empty set {} is a member of T{} for any semantic domain T.

In addition to the above, the some and every quantifiers can be used on sets. The quantifier

some x Œ A satisfies predicate(x)

returns true if there exists at least one element x in set A such that predicate(x) computes to true. If there is no such element

x, then the some quantifier’s result is false. If the some quantifier returns true, then variable x is left bound to any element

of A for which predicate(x) computes to true; if there is more than one such element x, then one of them is chosen arbitrarily.

For example,

some x Œ {3, 16, 19, 26} satisfies x mod 10 = 6

evaluates to true and leaves x set to either 16 or 26. Other examples include:

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