Appendix A: Core Syntax Quick Reference

The syntax of core language features is covered in this section. The data here is intended for use as a quick reference and examples will be kept to a minimum. For a more complete discussion of each item, see the appropriate chapter of the book. Our conventions will be

Italicized text to indicate a key term or phrase, and also to indicate a placeholder for some specified grammatical or lexical unit, such as an expression, statement, or sequence of characters.
Boldfaced text to indicate language keywords or reserved words.
[Bracketed text] to indicate optional grammatical units. Note that [unit1] [unit2] permits the absence of unit1 and unit2; or unit1 followed by unit2; or unit1; or unit2; while [unit1 [unit2]] permits the absence of unit1 and unit2; or unit1; or unit1 followed by unit2. The only exception is in the discussion of arrays and objects, which necessitate “real” brackets.
An ellipsis (...) to indicate repetition of the previous unit in the natural way.
Д to indicate a generic operator.

You can find the full specification for ECMAScript, which is the core of JavaScript, at www.ecma.ch, currently at http://www.ecma-international.org/publications/standards/Ecma-262.htm. Note, however, that there may be some slight aspects to the language discussed in this appendix that are part of the ad hoc standard implemented by browser vendors and not found in the ECMA specification.

Language Fundamentals

The following points are core principles of JavaScript:

Excess white space is ignored when outside of a regular expression literal or string.
Statements are terminated with a semicolon.
Semicolons are automatically inserted on lines with complete statements. (Returns imply semicolons for complete statements.)
Data is weakly typed.
References to identifiers are resolved using lexical (static) scoping. The one exception to this is class properties of the RegExp object, which are dynamically scoped.
Indices are enumerated beginning with zero.
There are four kinds of available objects: built-in objects, host (browser) objects, document objects and user-defined objects.
It is a prototype-based object oriented language (not class-based in its current incarnation).
Source code is interpreted.
Comments use C++ inline comment style // or C-style block comment /* */.
I/O is limited in most cases to interaction with Web documents and the user (no local filesystem or network access by default).

Language Versions

The versions of the various core languages and their relationships are listed in Tables A-1 through A-6.

Table A-1: Standard Versions of JavaScript
Standard Version	Description
ECMAScript Edition 1	First standardized version of JavaScript, based loosely on JavaScript 1.0 and JScript 1.0.
ECMAScript Edition 2	Standard version correcting errors within Edition 1 (and some very minor improvements).
ECMAScript Edition 3	More advanced language standard based on ECMAScript Edition 2. Includes regular expressions and exception handling. In widespread use.
ECMAScript Edition 4	New standard still unfinished at the time of this writing.

Table A-2: Correspondence Between Netscape Language and Browser Versions
Language Version	Browser Version
JavaScript 1.0	Netscape 2
JavaScript 1.1	Netscape 3
JavaScript 1.2	Netscape 4.0–4.05
JavaScript 1.3	Netscape 4.06–4.7
JavaScript 1.4	None
JavaScript 1.5	Netscape 6/7, Mozilla 1.0
JavaScript 2.0	Future versions of Mozilla-based browsers

Table A-3: Correspondence Between Microsoft Language and Browser Versions
Language Version	Browser Version
JScript 1.0	Internet Explorer 3.0
JScript 3.0	Internet Explorer 4.0
JScript 5.0	Internet Explorer 5.0
JScript 5.5	Internet Explorer 5.5
JScript 5.6	Internet Explorer 6.0

Table A-4: Approximate Correspondence Between Netscape and Microsoft Implementations
Language Version	Browser Version	Language Version	Browser Version
JavaScript 1.0	Netscape 2.0	JScript 1.0	Internet Explorer 3.0
JavaScript 1.3	Netscape 4.06	JScript 3.0	Internet Explorer 4.0
JavaScript 1.5	Netscape 6/7, Mozilla	JScript 5.5,5.6	Internet Explorer 5.5,6.0

Language Standards Conformance

Table A-5: Relationship Between Netscape JavaScript and ECMAScript
Netscape Version	Standard Version	Exceptions
JavaScript 1.0–1.2	Very loose conformance to ECMA-262 Edition 1	Many, especially with the Date object, and many extra features
JavaScript 1.3	Strict conformance to ECMA-262 Edition 1	Includes some extra features
JavaScript 1.4	Strict conformance to ECMA-262 Edition 1	Includes some extra features
JavaScript 1.5	Strict conformance to ECMA-262 Edition 3	Includes some extra features
JavaScript 2.0	Planned conformance to ECMA-262 Edition 4	Unknown

Table A-6: Relationship Between Microsoft JScript and ECMAScript
Microsoft Version	Standard Version	Exceptions
JScript 1.0	Very loose conformance to ECMA-262 Edition 1	Many, and some extra features
JScript 3.0	Strict conformance to ECMA-262 Edition 1	Includes some extra features
JScript 5.0	Strict conformance to ECMA-262 Edition 1	Includes many extra features
JScript 5.5	Strict conformance to ECMA-262 Edition 3	Includes some extra features
JScript 5.6	Strict conformance to ECMA-262 Edition 3	Includes some extra features