Errata

The last code sample for Number reads:

var value = 1234;
var binary_value = n.toString(2);

"n" is not defined in this example; assuming that it's meant to be a demonstration of the "toString" function, it should read:

var value = 1234;
var binary_value = value.toString(2);

instead.

Note from the Author or Editor:
Make change as per description; change from

var binary_value = n.toString(2);

to

var binary_value = value.toString(2);

The next to last line reads:

elt.innerHTMl = "Geolocation not supported in this browser";

It should read:

elt.innerHTML = "Geolocation not supported in this browser";

(The 'L' in "HTML" should be capitalized).

Note from the Author or Editor:
As per description, change innerHTMl to innerHTML

The code sample at the end of page 559 is written as:

$('#temp').load("us_weather_report.html", {zipcode:02134, units: 'F'});

This will not achieve the proper effect (and will be rejected in strict mode), because the zip code has a leading 0 and will be converted to octal in most implementations - as page 32 states, "you should never write an integer literal with a leading zero". The zip code should be enclosed in quotation marks:

$('#temp').load("us_weather_report.html", {zipcode:'02134', units: 'F'});

Note from the Author or Editor:
Enclose occurrences of 02134 in single quotes, as in detailed description.

var args = document.referrer.substring( ref.indexOf("?") + 1). split("&");

Flanagan, David (2011-04-18). JavaScript: The Definitive Guide (Definitive Guides) (p. 405). O'Reilly Media. Kindle Edition.

correct version:var args = document.referrer.substring( referrer.indexOf("?") + 1). split("&");

Note from the Author or Editor:
Change line to:

var args = document.referrer.substring(document.referrer.indexOf("?")+1).split("&");

The description of the function rotateAbout should be counterclockwise, not clockwise. We can write a code fragment to validate it, for example:

<canvas id="my_canvas_id" width=1000 height=1000></canvas>
<script>
var canvas = $('#my_canvas_id')[0];
var c = canvas.getContext('2d');
function rotateAbout(c, theta, x, y) {
var ct = Math.cos(theta), st = Math.sin(theta);
c.transform(ct, -st, st, ct, -x*ct-y*st+x, x*st-y*ct+y);
/* equal to
c.translate(x, y);
c.rotate(theta);
c.translate(-x, -y);
*/
}

rotateAbout(c, Math.PI, 500, 500);
c.beginPath();
c.moveTo(300, 300);
c.lineTo(200, 200);
c.lineTo(100, 200);
c.stroke();
</script>

original paragraph:
// Rotate theta radians clockwise around the point (x,y)
// This can also be accomplished with a translate,rotate,translate sequence function rotateAbout(c,theta,x,y) {
var ct = Math.cos(theta), st = Math.sin(theta);
c.transform(ct, -st, st, ct, -x*ct-y*st+x, x*st-y*ct+y); }

Note from the Author or Editor:
Change comment to read "counterclockwise" as per detailed description.

the JavaScript string "/type/test" is automatically converted

should probably read

the JavaScript string "/tmp/test" is automatically converted

Note from the Author or Editor:
Change "/type/test" to "/tmp/test" as per description of error.

// This is yet another way to get a list of all <name> tags. var
names3 = pt.element.*;

probably should be

// This is yet another way to get a list of all <name> tags.
var names3 = pt.element.*;

Note from the Author or Editor:
Add line break after "tags."

I couldn?t get function hide to work. Instead, I used:

function hide(event) {
var target = event.target ? event.target : event.srcElement;

//srcElement needed for IE8, target for Chrome and FireFox

target.style.visibility = "hidden";
}

Note from the Author or Editor:
Changed code for function to:

function hide(event) {
// srcElement needed for IE8, target for Chrome and Firefox
var target = event.target ? event.target : event.srcElement;
target.style.visibility = "hidden";
}

In the sentence starting "If the textBaseline is 'center' . . . " should read "If the textBaseline is 'middle' . . . " . Page 873 says that there is no 'center' as a legal value of textBaseline.

Note from the Author or Editor:
Change "center" to "middle" as per description of error.

The <tr> lines for Repayment period and Zipcode do not have matching </tr> codes. Although the code seems to work fine without them, I've always been told that it's "good programming practice" to include them. (I've also downloaded the code from the website, and found it also has the same problem.)

Note from the Author or Editor:
Added </tr> tags at end of the lines:

In section 7.6 "Iterating Arrays", a code example is given which shows a technique for "exclud[ing] null, undefined, and nonexistent elements" while iterating through a sparse array. The important bit is:

if (!a[i]) continue; // Skip null, undefined, and nonexistent elements

However, this conditional will also exclude falsy elements, which does not appear to match the intention of the technique. Either this should be mentioned in the text or the conditional should be changed.

Note from the Author or Editor:
Change if (!a[i]) continue; to:
if (a[i] === null || a[i] === undefined)

The last paragraph starts with the following sentence:

"+, ==, != and the relational operators are the only ones that perform this special kind of string-to-primitive conversions"

I believe that instead of "string-to-primitive conversions" it should've been "object-to-primitive conversions". Two reasons:
1) The specific conversion the author is probably referring to is described above using the "object-to-primitive" term
2) String is already a primitive, so the "string-to-primitive conversion" term makes no sense.

Note from the Author or Editor:
Change text to read "...perform this special kind of object-to-primitive conversions"

Section 4.9.4: The InstanceOf Operator

Last sentence of 2nd text paragraph (ignoring code sample) reads: If the right-hand side is not a function, it throws a TypeError.

I believe "function" should be "object" or "Class of Objects".

Note from the Author or Editor:
Reword to "If the right-hand side is not a class of objects,..."

The examples given for the "host" and "hostname" location properties erroneously include the URI schema (erroneously referred to as the "protocol" by JavaScript). The hostname property includes only of the name, domain-name and top-level domain of the host. The host includes the hostname and port number (if other than the default for the protocol indicated by the scheme).
So...
"http://www.oreilly.com:1234" should be "www.oreilly.com:1234"
and
"http://www.oreilly.com" should be "www.oreilly.com"

Note from the Author or Editor:
Change as per description:
"http://www.oreilly.com:1234" should be "www.oreilly.com:1234"
and
"http://www.oreilly.com" should be "www.oreilly.com"

The add() methods for both Set and NonNullSet each return a this reference in order to support method chaining. However, the add() method of sets created by means of filteredSetSubclass() does not.

Note from the Author or Editor:
Change code to read:

return superclass.prototype.add.apply(this, arguments);

The for/in loop neglects to declare the variable 'name' with 'var'. 'name' becomes a global variable.

Note from the Author or Editor:
change loop to read:
for(var name in namesToValues) {

In the fuction "hide", a semicolon is missing in the following line:

e.style.display = "non" // hide element and use its space

Note from the Author or Editor:
Line should read:

e.style.display = "non"; // hide element and use its space

The final example on the page uses partial() to define a function that returns the last "character" of a string. The example uses the substr() function. However, the reference entry for substr() on pg. 849 identifies this function as nonstandard and deprecated.

Instead:
String.prototype.last = partial(String.prototype.slice, -1);

Note from the Author or Editor:
Replace
String.prototype.last = partial(String.prototype.substr, -1, 1);
with
String.prototype.last = partial(String.prototype.slice, -1);

Same issue as pg. 130. Test should be: m > n

Note from the Author or Editor:
Change m >= n to m > n

As Ben Petersen previously noted, this sample code does not work:
r.foreach(console.log)

According to the following StackOverflow entry, the problem is related to aliasing the console.log function:
http://stackoverflow.com/questions/5133649/alias-to-chrome-console-log

The simple fix--bind to the 'console' object:
r.foreach(console.log.bind(console))

Another more verbose solution--avoid the alias:
r.foreach(function(x) {console.log(x);})

The problem occurs in Chrome and Safari, although Ben says Firefox works.

Note from the Author or Editor:
Change r.foreach(console.log) to the verbose solution: r.forEach(function(x) {console.log(x);})

2nd sentence states that the URL in open() is relative to the URL of the document that contains the script that is calling open(). Need to add to this sentence, "... unless the document contains a <base> tag, in which case the URL is relative to that."

Note that some older browsers (eg, Netscape 7.02) do not respect this.

Note from the Author or Editor:
Add text to sentence as per description:

, unless the document contains a <base> tag, in which case the URL is relative to that. (Some very old browsers, e.g., Netscape 7.02, do not respect this.)

The function isArrayLike() strives to weed out objects that are not array-like, particularly those simply possessing a length property. The comments indicate that strings are rejected by the function. This is true for string primitives but not for String objects which will evaluate to true by isArrayLike().

Furthermore, the upper limit for the value of length is not quite right. As pg. 141 correctly points at, and as the erratum reported for pg. 143 highlights, the length must be strictly less than Math.pow(2, 32) -1. So the function should either test:
o.length < Math.pow(2, 32) - 1
or
o.length <= Math.pow(2, 32) - 2

Note from the Author or Editor:
Change line from:
o.length < 4294967296) // o.length < 2^32

to:

o.length< 4294967295) // o.length &lt; 2^32 - 1

The book states that the string indexOf() and lastIndexOf() methods work like the corresponding array methods do. This may be true overall, but one specific difference is that the string versions don't accept negative values for the 2nd optional position argument.

According to section 15.5.4.7 (and 15.5.4.8) of the standard, both indexOf() and lastIndexOf() compute their starting index in terms of max(pos, 0), where pos is the result of ToInteger(position). Consequently, a negative position is simply treated as 0 for the string versions unlike the array versions.

Note from the Author or Editor:
Change text to read "methods that work like these array methods, except that a negative second argument is treated as zero."

"When any identifier appears by itself in a program, JavaScript assumes it is a variable and looks up its value."

Until here, the information is correct. The topic 3.10.3 (Scope Chain) explain how the variable is look up through the source code.

"If no variable with that name exists, the expression evaluates to the undefined value. In the strict mode of ECMA 5, however, an attempt to evaluate a nonexistent variable throws a ReferenceError instead."

Even in EcmaScript 3, a nonexistent variable throws a ReferenceError. I used the following code to test.

try {
console.log(nonexistVariable);
}
catch (e) {
console.log(e.toString());
}

I got the following error: "ReferenceError: nonexistVariable is not defined". (All browsers throws the ReferenceError, but the messages are slightly different).

Note from the Author or Editor:
Replace sentence starting "If no variable..." with: If no variable with that name exists, an attempt to evaluate a nonexistent variable throws a ReferenceError instead.

The following phrase is confusing: "Strings are not objects, though, so why do they have properties?".

This affirmation is not true for every case. For example, in the following code, myString is an object:

var myString = new String("this is my string");

I think that the text could be modified to: "Primitive strings are not objects, though, so why do they have properties?".
Then, the author must explain the difference between primitive strings, and string objects.

The String documentation on String global object has a topic, called "Distinction between string primitives and String objects" that is superb. The following sample code is enlightening:

var s_prim = "foo";
var s_obj = new String(s_prim);

console.log(typeof s_prim); // Logs "string"
console.log(typeof s_obj); // Logs "object"

Note from the Author or Editor:
Change "Strings are not objects" to "Primitive strings are not objects"

Number.MAX_VALUE + 1 evaluates to 1.7976931348623157e+308 instead of Infinity, like the affirmation in the code comment. The result of the expression Number.MAX_VALUE + 1 is equal to Number.MAX_VALUE. The equality can be verified with the following test:
Number.MAX_VALUE + 1 === Number.MAX_VALUE that returns true.

-Number.MIN_VALUE - 1 evaluates to -1.7976931348623157e+308 instead of -Infinity, like the affirmation in the code comment. The result of the expression -Number.MAX_VALUE - 1 is equal to -Number.MAX_VALUE. The equality can be verified with the following test:
-Number.MAX_VALUE - 1 === -Number.MAX_VALUE that returns true.

Note from the Author or Editor:
Replace Number.MAX_VALUE + 1 with Number.MAX_VALUE * 2 and Number.MIN_VALUE -1 with Number.MIN_VALUE * 2; this does results in Infinity

The text states that objects created by means of Object.create() have a constructor property that refers to the Object() constructor. However, both Chrome (23.0.1271.64) and Safari (5.1.7) report:
Object.create(new Date()).constructor =>
function Date() { [native code] }

The book is correct, however, in explaining that constructor.prototype here does not refer to the correct prototype:
var d = Object.create(new Date());

d.constructor.prototype === Object.getPrototypeOf(d) => false

d.constructor.prototype === Object.getPrototypeOf(Object.getPrototypeOf(d)) => true

Note from the Author or Editor:
Change "Note that objects created by object literals or by Object.create() have a constructor property that refers to the Object() constructor."

to:

"Note that objects created by object literals or by Object.create() with an object literal as their first argument have a constructor property that refers to the Object() constructor."

The comment in the code and the error message thrown state that the new value must be larger than the existing value. However, the code accepts equal values in the 'if' test: n >= this.$n

Strictly speaking, the test should be: n > this.$n

Note from the Author or Editor:
Change line to if (n > this.$n) this.$n = n;

The following code is incorrect:

var isArray = Function.isArray || function(o) {
return typeof o === "object" &&
Object.prototype.toString.call(o) === "[object Array]";
};

The Function.isArray should be Array.isArray so that it reads as:

var isArray = Array.isArray || function(o) {
return typeof o === "object" &&
Object.prototype.toString.call(o) === "[object Array]";
};

Note from the Author or Editor:
Change Function.isArray to Array.isArray as per description of error.

The code in function merge() should have parentheses surrounding prop rather than square brackets in the line:

if (o.hasOwnProperty(prop)) continue;

NOT

if (o.hasOwnProperty[prop]) continue;

Also, in all of the examples on page 127, it would be better to include a var expression inside the for/in loop. That is:

for (var prop in p)

instead of

for (prop in p)

Note from the Author or Editor:
Square brackets -> parentheses is a duplicate; change
for (prop in p)
to
for (var prop in p)
in all examples on page 127; also change
for (p in o)
to
for (var p in o)
in examples on pages 126 and 127.

end of script in the example code:
document.write("<br>Accessed on: " + new Date());

should end with closing tag.
document.write("<br>Accessed on: " + new Date() + "</p>");

Browsers append </p> automatically though, we should not rely on such behavior.

Note from the Author or Editor:
Change as specified in description of error:

The book states:

"The Document object also has a URL property, which is a static string that holds the URL of the document when it was first loaded. If you navigate to fragment identifiers (like ?#table-of-contents?) within the document, the Location object is updated to reflect this, but the document.URL property remains unchanged."

This is untrue, document.URL is same as location.href, it does change to reflect the fragment identifier.

Note from the Author or Editor:
Change text to read: If you navigate to fragment identifiers (like ?#table-of-contents?) within the document, both the Location object and the document.URL property are updated to reflect this.

The statement for displaying the modal dialog box is written:

var p = showModalDialog("multiprompt.htm", ['Enter 3D point coordinates','x','y','z'], "dialogwidth:400; dialogheight:300; resizable:yes");

Firefox displays the modal dialog correctly with this statement, but IE8 requires units for the height and width of the dialog:

var p = showModalDialog("multiprompt.htm", ['Enter 3D point coordinates','x','y','z'], "dialogwidth:400px; dialogheight:300px; resizable:yes");

Also, the IE JavaScript safety wall prevents the "Okay" and "Close" buttons from working correctly.

Note from the Author or Editor:
Add px to the dimensions as described in error:

var p = showModalDialog("multiprompt.html",
["Enter 3D point coordinates", "x", "y", "z"],
"dialogwidth:400px; dialogheight:300px; resizable:yes");

The book states that the code

location.search = "?page=" + (pagenum+1);

loads the next page. In reality, it only reloads the same page with the new query string that was written above.

Note from the Author or Editor:
Change line to read:

location.search = "?sold=" + (sold+1); // reload page with new query string

(changed from "page" to "sold" to avoid confusion with prevoius example)

Mr.Flanagan wrote that when XML is being used, the actual code in a <script> tag should be enclosed within the tags
<![CDATA[ ... ]]>. He meant to write <!--[CDATA[ ... ]] -->. But even the corrected version works only in IE8. The corrected version makes the JavaScript invisible to FireFox (at this site, Mozilla/5.0 (Windows NT 5.1; rv:10.0) Gecko/20100101 Firefox/10.0).

Note from the Author or Editor:
Change example to:
<script>
// <![CDATA[
// Your JavaScript code goes here
// ]]>
</script>

Text to the left of the matched substring is $`, not $'.

Note from the Author or Editor:
Change first column in the row with "The text to the left of the matched substring" to $`

In the example:

p:nth-child(3n+1):text(JavaScript):not(:has(a))

shouldn't "text" be "contains"? "text" searches for [type="text"] while "contains" searches for its textual argument.

Note from the Author or Editor:
Replace
p:nth-child(3n+1):text(JavaScript):not(:has(a))

with:
p:nth-child(3n+1):contains(JavaScript):not(:has(a))

The text refers to the non-existent XMLHttpRequest method setOverrideMimeType(), instead of overrideMimeType(), which is probably what is intended.

Note from the Author or Editor:
Change setOverrideMimeType() to overrideMimeType()

As is stated in the penultimate para of the same page, the font-size property name should be quoted, ie

"font-size": 10

instead of

font-size: 10

Note from the Author or Editor:
Change as described in error:
"font-size": 10

I found that the code for the timer utility function "invoke" works as shown in IE9, Chrome and Safari, but Firefox 10.0.2 throws an error message "repeat is not defined" when using all four arguments.

I think this is because the function repeat is defined within an else clause. According to page 91 (penultimate para) of the book, this is not allowed (or at least not portable). The error went away when I moved the function definition below the closing curly bracket of the else.

Note from the Author or Editor:
Moved the repeat function below the closing brace of the "else" clause, as in the description of error.

variable is shadowing A NEW variable by the same name:

"A NEW" should read "AN OLD".

Note from the Author or Editor:
Change text from:

This matters only when the new variable is shadowing a new variable by the same name:

to:

This matters only when the new variable is shadowing an old variable by the same name:

Should "ten" be replaced by "one hundred"? The text reads:

"version number times ten. Pass 170 to select JavaScript 1.7"

Note from the Author or Editor:
Replace "version number times ten." with "version number times 100." (Numbers greater than ten are written using digits per O'Reilly Style guide.)

It could be worth noting, as a comment in the JavaScript code, that the line appending the script node should be preceded by setAttribute('type', 'text/javascript') when the the JavaScript code is to be used together with XHTML code.

Note from the Author or Editor:
Added this comment:

// If you use the JavaScript code together with XHTML, add
// script.setAttribute('type', 'text/javascript');

The min property is described as "A maximum valid value for this Input element." This should probably say "A minimum valid ..."

Note from the Author or Editor:
Make change as in description of error:

"A maximum valid value for this input. element." should become
"A minimum valid value for this input. element.

The code example:

var square = function(x) { return x * x; }

should include a final semi-colon at the end of the line to reflect best practices as well as to continue the correlation between object and array literals that precede it (where this syntax is used properly):

var square = function(x) { return x * x; };

Note from the Author or Editor:
Include a final semi-colon at the end of the line:

var square = function(x) { return x * x; };

(The same example on page 7, though split across several lines, has a semicolon after the closing brace.)

ymin assigned twice, second time must be: ymax=parseFloat(...);
Following line (assigning points) must be removed, because points not used any further and "data-points" not in HTML.

Note from the Author or Editor:
Code should read:
var ymax = parseFloat(elt.getAttribute("data-ymax"));
and remove the line starting "var points "

The examples of array.splice() give false return results. It should be:

var a= [1,2,3,4,5,6,7,8];
a.splice(1,2); // Returns [2,3]; a is [1,4,5,6,7,8]
a.splice(1,1); // Returns [4]; a is 1,5,6,7,8]
a.splice(1,0,2,3) //Returns []; a= 1,2,3,5,6,7,8

Note from the Author or Editor:
Add this as the first example:
a.splice(4); // Returns [5,6,7,8]; a is [1,2,3,4]
Then all the subsequent examples are correct.

ECMAScript 5 reserves the keywords "import" and "export" not the keywords "imports" and "exports".

Note from the Author or Editor:
Make correction as specified in description.

The expression for the return statement in the example is "x !== undefined && x != null". Either use !== for both comparisons or simplify it to x != null.

Note from the Author or Editor:
Change x!= null to x !== null (consistent, and best practice)

The comment describing the one-line string written on 3 lines is nested within the string literal. This makes the comment part of the string literal and the backslash is not part of a line continuation.

Note from the Author or Editor:
Move comment to precede the strings:

// A string representing 2 lines written on one line
"two\nlines"
// A one-line string written on 3 lines. ECMAScript 5 only.
"one\
long\
line"

The provided code does not work in Chrome, though is fine in Firefox. The snippet that throws errors in chrome is: foreach: function(f) {for(var x = Math.ceil(this.from); x <= this.to; x++ ) f(x);}

Note from the Author or Editor:
Change r.foreach(console.log) to the verbose solution: r.forEach(function(x) {console.log(x);})

At least in 'WebKit' you need to call

document.createEvent('Events')

to create a simple event object (the book states that document.createEvent('event') will do).

Note from the Author or Editor:
Please fix.

On the methods of HTMLOptionsCollection, there is the "add" method.
It says that the second parameter is optional. This is not true in all browsers. In FireFox (tested on 3.6.18, 4.0 and 5.0.1), the 2nd argument is REQUIRED. You must pass null if you want to add at the end.

Here is the message that Firefox shows:

Error: uncaught exception: [Exception... "Not enough arguments" nsresult: "0x80570001 (NS_ERROR_XPC_NOT_ENOUGH_ARGS)" location: "..." data: no]

The same problem happens on page 987, on the add method.

If the specs/RFC (if any) define that the 2nd parameter is indeed optional, there should be a note on the book saying that Firefox is buggy. If the specs/RFC define that the 2nd parameter is mandatory, the book should be corrected.

Thanks,
Claudio Neves

Note from the Author or Editor:
Add text at end of paragraph: In some older browsers such as Firefox 5.0.1, the second argument is required.

'Any <span> with "warning" and "fatal" in its class' shoud read 'Any <span> with "fatal" and "error" in its class'

In Example 8-3, the nested patched_extend(o) function references the protoprops variable defined in its surrounding function, but the assignment of an array of strings to the protoprops variable is unreachable code. The declaration of the protoprops variable will be hoisted, but since the unnamed outer function will always return either the extend(o) or the patched_extend(o) function before the assignment statement itself is executed, the value of protoprops should always be undefined.

Note from the Author or Editor:
This is another good catch.

Move the 4 lines beginning with the blank line before this one:

// This is the list of...

Up so that they appear right after this line:

// properties of Object.prototype.

You should end up with a 4-line comment block, followed by a blank line,
followed by a one line comment, followed by 2 lines beginning "var
protoprops = " followed by the line "return function patched_extend(0)
{" and all the code that follows that. The example should still end
with the line "}());"

The last sentence says that the default attribute values of absent members are false or null, but ECMAScript language defines them false or "undefined", not null. This definition is shown as Table-7 on ECMA-262 edition 5.1, within the Object Type section (8.6.1 actually).

Note from the Author or Editor:
Change "false or null" to "false or undefined"

Page 503; Example 18-5, first paragraph following:

"HTML forms generate POST requests by default."

Is that true? Perhaps XMLHTTPRequest does, but do
HTML forms default to POST?

Page 502 and 503: Example 18-4: encodeFormData() function.

I believe there are other locations where this procedure
is used (decoding data, etc.).

The code indicates that to *encode* data, first replace spaces with "+"
then encodeURIComponent. To *decode* submitted data, first
decodeURIComponent and then replace "+" with space (I am *sure* I saw
that decoding somewhere, using 'unescape' - but it seems to be wrong).

Done that way, spaces and "+"s in the original text are mixed and
cannot be unmixed.

encodeURIComponent appears *not* to act precisely the way a form
submission acts in encoding items. In submission of a real form
on an HTML page, submitted data first has "+"s encoded (HEXed/escaped)
but SPACES ARE LEFT ALONE (not escaped). After that step (escaping)
spaces are converted to "+" as the final encoding step. Apparently
this is a hold over from old formats when only plain text (no "+"s!)
with spaces was expected (if that is the case, then just convert
spaces to + to send it without problems and there is no mixing of
"+" and space as the original text had no "+"s). That is the data
(first escape some characters, including "+" but EXCLUDING spaces,
and then change spaces to "+").

I guess, if done now, both "+" and spaces would simply be escaped.

On the other hand, encodeURIComponent seems to escape both spaces
AND "+" - a bit different from www-form encoding (in which case
don't do any of the space/+ conversions in creating data, there
won't be any problem or spaces or "+" after endodeURIComponent).
Hopefully servers will handle decoding of submitted data (they
will try first to convert "+" to space, but find none, and then
unescape the result ... and it comes out right). On the other hand,
I am sure there is code in 'Javascript, The Definitive Guide" for
DECODING responses and if the response is sent back 'www-form-encoded'
one has to decode it properly (first change "+" to space and *then*
unescape which will recover any "+"s in the original data).

Note from the Author or Editor:
In the first block of code on page 503, change these lines:

name = encodeURIComponent(name.replace(" ", "+")); // Encode name
value = encodeURIComponent(value.replace(" ", "+")); // Encode value

To:
name = encodeURIComponent(name).replace("%20", "+"); // Encode name
value = encodeURIComponent(value).replace("%20", "+"); // Encode value

In the last paragraph of page 503, cut the lines:

HTML forms generate POST requests by default, but they can also make
GET requests. (When the purpose...than POST.)

And replace them with these:

Form data can also be submitted using a GET request, and when the
purpose of a form submission is to make a read-only query, GET is
more appropriate than POST.

In the 10th line of example there is comma missing after } (after third parameter of requestFileSystem).

Note from the Author or Editor:
Change these two lines:

// Use fs here
}

To add a comma after the brace:

// Use fs here
},

<pre>
Page 208: Section 9.4: First paragraph:

... an object inherits properties from its prototype, even if the prototype
changes after the object is created.

is at least misleading. 'prototype' is the name of a pointer/reference to a
object which contains the prototypical properties since arrays/objects are
referenced by pointer/reference (section 3.7).

This is a perfect example of pointer/reference access to one object using
different copies of the same pointer/reference.

I think saying 'even if the prototype's properties, but not the actual
prototype, changes, since the prototype is referenced by pointer/reference ...'
would be clearer and let one see just why changes in the prototype do affect
old objects.


SAMPLE:
=======
I will look at an object which is an instance of a class for which the
prototype is created as a property of the constructor. I will use 'print'
for output (the spider monkey stand alone interpreter's output function).


If you change the prototype itself, the POINTER to the object of
prototypical values, then new objects use the new prototype but
*OLD OBJECTS USE THE OLD PROTOTYPE*. The new objects (objects created after
the prototype changes) contain pointers to the new object containing the
new prototype values while the old objects use the old prototype
(pointer/reference to the old prototype's object).

function Test1() {};Test1.prototype={a:1,b:2}

T=new Test1
print(T.a);print(T.b);print(T.c)
Test1.prototype={a:10,b:20,c:30}
U=new Test1
print(T.a);print(T.b);print(T.c)
print(U.a);print(U.b);print(U.c)

gives 1, 2, undefined [original T before the prototype has changed]
1,2, undefined [original T AFTER the prototype has changed] <--
10,20,30 [U - created AFTER the prototype has changed]

T retains the old prototype, i.e. the pointer to the old prototype's
object.


On the other hand, if you change the CONTENTS of the prototype object
but not the prototype (i.e. the pointer/object containing the values):

function Test2() {};Test2.prototype={a:1,b:2}

V=new Test2
print(V.a);print(V.b);print(V.c)
Test2.prototype.a=10;Test2.prototype.b=20;Test2.prototype.c=30
W=new Test2
print(V.a);print(V.b);print(V.c)
print(W.a);print(W.b);print(W.c)

Then one gets:
1, 2, undefined [original V before the prototype has changed]
10,20,30 [original V AFTER the prototype has changed] <--
10,20,30 [W - created AFTER the prototype has changed]


If an instance of an class contained a reference to its constructor
(instead of the constructor's prototype) and actually used that to access
the prototype object of its class/constructor (rather than having a
pointer to the prototype object used when it was constructed itself)
then one could change the prototype object (not just its contents)
(as a property of the constructor) and the changed prototype would affect
both new *and old* instances:

function Test3() {this.constructor=Test3}; Test3.prototype={a:1,b:2}

X=new Test3
print(X.constructor.prototype.a);print(X.constructor.prototype.b);print(X.constructor.prototype.c)
Test3.prototype={a:10,b:20,c:30}
Y=new Test3
print(X.constructor.prototype.a);print(X.constructor.prototype.b);print(X.constructor.prototype.c)
print(Y.constructor.prototype.a);print(Y.constructor.prototype.b);print(Y.constructor.prototype.c)

produces:
1, 2, undefined [original X before the prototype has changed]
10,20,30 [original X AFTER the prototype has changed]
10,20,30 [Y - created AFTER the prototype has changed]


Now I wonder what intricacies are created when a constructor which is
an internal function to another is called - if the constructor's
'prototype' is set equal (f.prototype=p) to an internal variable of
the containing function ... or various properties of the prototypical
object are set equal to internal variables ....
</pre>

Note from the Author or Editor:
Okay, change "even if the prototype changes" to "even if the
properties of the prototype change"

Object.prototype.isPrototypeOf(o) // => true: p inherits from Object.prototype

Should read,

Object.prototype.isPrototypeOf(o) // => true: o inherits from Object.prototype

Note from the Author or Editor:
The reader is correct that there is a problem, but the
proposed solution is wrong.

Change the line:

Object.prototype.isPrototypeOf(o) // =>; true: p inherits from Object.prototype

To:

Object.prototype.isPrototypeOf(p) // =>; true: p inherits from Object.prototype

The function "union"'s comment section notes that "If o and p have properties by the same name, the values from o are used". It should read "the values from p are used".

Note from the Author or Editor:
change the comment as the reader suggests

"... and whose name is the HTMLElement ..."
should read:
and whose value is the HTMLElement

Note from the Author or Editor:
yes, make that change.

The second sentence of this paragraph reads:

"All indexes are property names, but only property names that are integers between 0 and 2^32 - 1 are indexes."

This is misleading. According to the ECMAScript spec (section 15.4, both the 3rd and 5th edition):

"A property name P (in the form of a String value) is an array index if and only if ToString(ToUint32(P)) is equal to P and ToUint32(P) is not equal to 2^32 - 1."

So the second sentence of your paragraph should read:

"All indexes are property names, but only property names that are integers between 0 and 2^32 - 2 are indexes."

Thanks so much for writing this book!

Note from the Author or Editor:
Good catch! Change
2<superscript>32</superscript>-1
to
2<superscript>32</superscript>-2