JavaScript: The Good Parts by Douglas Crockford Publisher: O ...

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2 the space between var and that cannot be removed, but the other spaces can be removed. JavaScript offers two forms of comments, block comments formed with /* */ and line-ending comments starting with //. Comments should be used liberally to improve the readability of your programs. Take care that the comments always accurately describe the code. Obsolete comments are worse than no comments. The /* */ form of block comments came from a language called PL/I. PL/I chose those strange pairs as the symbols for comments because they were unlikely to occur in that language's programs, except perhaps in string literals. In JavaScript, those pairs can also occur in regular expression literals, so block comments are not safe for commenting out blocks of code. For example: /* */ var rm_a = /a*/.match(s); causes a syntax error. So, it is recommended that /* */ comments be avoided and // comments be used instead. In this book, // will be used exclusively. 2
Chapter 2. Grammar I know it well: I read it in the grammar long ago. â William Shakespeare, The Tragedy of Titus Andronicus This chapter introduces the grammar of the good parts of JavaScript, presenting a quick overview of how the language is structured. We will represent the grammar with railroad diagrams. The rules for interpreting these diagrams are simple: • You start on the left edge and follow the tracks to the right edge. • As you go, you will encounter literals in ovals, and rules or descriptions in rectangles. • Any sequence that can be made by following the tracks is legal. • Any sequence that cannot be made by following the tracks is not legal. • Railroad diagrams with one bar at each end allow whitespace to be inserted between any pair of tokens. Railroad diagrams with two bars at each end do not. The grammar of the good parts presented in this chapter is significantly simpler than the grammar of the whole language. 2.1. Whitespace Whitespace can take the form of formatting characters or comments. Whitespace is usually insignificant, but it is occasionally necessary to use whitespace to separate sequences of characters that would otherwise be combined into a single token. For example, in: var that = this; 1 1
Page 1 and 2: JavaScript: The Good Parts by Dougl
Page 5 and 6: Section C.9. Expression Statements
Page 9 and 10: Dedication For the Lads: Clement, P
Page 11 and 12: Preface If we offend, it is with ou
Page 13 and 14: I want to thank the people I worked
Page 15 and 16: Chapter 1. Good Parts ...setting th
Page 17 and 18: Chapter 1. Good Parts ...setting th
Page 19 and 20: 1.2. Analyzing JavaScript JavaScrip
Page 21 and 22: 1.3. A Simple Testing Ground If you
Page 23: Chapter 2. Grammar I know it well:
Page 27 and 28: 2.2. Names A name is a letter optio
Page 29 and 30: 2.3. Numbers JavaScript has a singl
Page 31 and 32: 2.4. Strings A string literal can b
Page 33 and 34: 2.5. Statements A compilation unit
Page 35 and 36: The switch statement performs a mul
Page 37 and 38: The try statement executes a block
Page 39 and 40: 2.6. Expressions The simplest expre
Page 41 and 42: Invocation causes the execution of
Page 43 and 44: 2.7. Literals Object literals are a
Page 45 and 46: 2.8. Functions A function literal d
Page 47 and 48: Chapter 3. Objects Upon a homely ob
Page 49 and 50: Chapter 3. Objects Upon a homely ob
Page 51 and 52: 3.2. Retrieval Values can be retrie
Page 53 and 54: 3.3. Update A value in an object ca
Page 55 and 56: 3.4. Reference Objects are passed a
Page 57 and 58: 3.5. Prototype Every object is link
Page 59 and 60: 3.6. Reflection It is easy to inspe
Page 61 and 62: 3.7. Enumeration The for in stateme
Page 63 and 64: 3.8. Delete The delete operator can
Page 65 and 66: 3.9. Global Abatement JavaScript ma
Page 67 and 68: Chapter 4. Functions Why, every fau
Page 69 and 70: Chapter 4. Functions Why, every fau
Page 71 and 72: 4.2. Function Literal Function obje
Page 73 and 74: 4.3. Invocation Invoking a function
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document.writeln(myQuo.get_status(
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4.4. Arguments A bonus parameter th
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4.5. Return When a function is invo
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4.6. Exceptions JavaScript provides
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4.7. Augmenting Types JavaScript al
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4.8. Recursion A recursive function
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4.9. Scope Scope in a programming l
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4.10. Closure The good news about s
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}; } } // END BAD EXAMPLE The add_t
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4.11. Callbacks Functions can make
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4.12. Module We can use functions a
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4.13. Cascade Some methods do not h
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4.14. Curry Functions are values, a
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4.15. Memoization Functions can use
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Chapter 5. Inheritance Divides one
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eturn s; }; Cat.prototype.get_name
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Chapter 5. Inheritance Divides one
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eturn s; }; Cat.prototype.get_name
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5.2. Object Specifiers It sometimes
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5.3. Prototypal In a purely prototy
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5.4. Functional One weakness of the
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}; for (i = 0; i < n; i += 1) { if
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5.5. Parts We can compose objects o
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Chapter 6. Arrays Thee I'll chase h
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Chapter 6. Arrays Thee I'll chase h
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6.2. Length Every array has a lengt
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6.3. Delete Since JavaScript's arra
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6.4. Enumeration Since JavaScript's
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6.5. Confusion A common error in Ja
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6.6. Methods JavaScript provides a
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6.7. Dimensions JavaScript arrays u
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Chapter 7. Regular Expressions Wher
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Regular expressions cannot be broke
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The $ represents the end of the str
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Chapter 7. Regular Expressions Wher
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Regular expressions cannot be broke
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The $ represents the end of the str
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7.2. Construction There are two way
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7.3. Elements Let's look more close
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The backslash character indicates e
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Code View: (?:!|"|#|\$|%|&|'|$|$|
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Chapter 8. Methods Though this be m
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array.slice(start, end ) The slice
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is not guaranteed to produce the co
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Function Number var a = ['a', 'b',
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Object RegExp The most common case,
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String // [3] regexp.test(string )
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it produces an array of all the mat
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is 'and' var c = text.slice(-5); //
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Chapter 9. Style Here is a silly st
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i = 0; // Set i to zero. In JavaScr
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Chapter 10. Beautiful Features Thus
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Appendix A. Awful Parts That will p
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Appendix A. Awful Parts That will p
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A.2. Scope JavaScript's syntax come
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A.3. Semicolon Insertion JavaScript
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A.4. Reserved Words The following w
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A.5. Unicode JavaScript was designe
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A.6. typeof The typeof operator ret
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A.7. parseInt parseInt is a functio
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A.8. + The + operator can add or co
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A.9. Floating Point Binary floating
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A.10. NaN The value NaN is a specia
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A.11. Phony Arrays JavaScript does
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A.12. Falsy Values JavaScript has a
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A.13. hasOwnProperty In Chapter 3,
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A.14. Object JavaScript's objects a
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Appendix B. Bad Parts And, I pray t
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Appendix B. Bad Parts And, I pray t
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B.2. with Statement JavaScript has
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B.3. eval The eval function passes
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B.4. continue Statement The continu
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B.5. switch Fall Through The switch
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B.6. Block-less Statements An if or
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B.7. ++ -- The increment and decrem
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B.8. Bitwise Operators JavaScript h
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B.9. The function Statement Versus
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B.10. Typed Wrappers JavaScript has
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B.11. new JavaScript's new operator
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B.12. void In many languages, void
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Appendix C. JSLint What error drive
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Appendix C. JSLint What error drive
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C.2. Members Since JavaScript is a
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C.3. Options The implementation of
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C.4. Semicolon JavaScript uses a C-
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C.5. Line Breaking As a further def
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C.6. Comma The comma operator can l
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C.7. Required Blocks JSLint expects
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C.8. Forbidden Blocks In many langu
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C.9. Expression Statements An expre
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C.10. for in Statement The for in s
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C.11. switch Statement A common err
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C.12. var Statement JavaScript allo
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C.13. with Statement The with state
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C.14. = JSLint does not expect to s
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C.15. == and != The == and != opera
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C.16. Labels JavaScript allows any
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C.17. Unreachable Code JSLint expec
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C.18. Confusing Pluses and Minuses
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C.19. ++ and -- The ++ (increment)
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C.20. Bitwise Operators JavaScript
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C.21. eval Is Evil The eval functio
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C.22. void In most C-like languages
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C.23. Regular Expressions Regular e
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C.24. Constructors and new Construc
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C.25. Not Looked For JSLint does no
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C.26. HTML JSLint is able to handle
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C.27. JSON JSLint can also check th
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C.28. Report If JSLint is able to c
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Appendix D. Syntax Diagrams Thou ma
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3 3
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5 5
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7 7
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11 11
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Appendix E. JSON Farewell: the leis
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That's it. That is all of JSON. JSO
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Appendix E. JSON Farewell: the leis
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That's it. That is all of JSON. JSO
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E.2. Using JSON Securely JSON is pa
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E.3. A JSON Parser This is an imple
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}, } } error("Bad string"); white =
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} error("Syntax error"); // If ther
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Appendix. Colophon The animal on th
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Index [SYMBOL] [A] [B] [C] [D] [E]
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