Errata

The const declarations for the Unix-style file permissions are missing the equals signs. Also their values are wrong: the correct values are 4 for read, 2 for write and 1 for execute.

Note from the Author or Editor:
Confirmed. This has been corrected in the text.

Testing for multiple flags requires a more complicated expression. Instead of

let hasReadAndExecute = p & (FLAG_READ | FLAG_EXECUTE);

it should be

let mask = FLAG_READ | FLAG_EXECUTE;
let hasReadAndExecute = (p & mask) === mask;

Or rename the variable to hasReadOrExecute, but that is not likely to have been the intention.

Note from the Author or Editor:
Confirmed. This has been corrected in the text.

In while loop, instead of using a comma in the condition use &&. Also, the interpolated expression in the last message is incorrect. See below:

while((n = nums[i]) < 10 && i++ < nums.length) {
console.log(`Number less than 10: ${n}.`);
}
console.log(`Number greater than 10 found: ${n}.`);
console.log(`${nums.length - i} numbers remain.`);

Note from the Author or Editor:
Corrected in text.

In The Error Object example, the console.error message is missing the closing backtick.

console.error(`Error: ${validatedEmail.message});

should be

console.error(`Error: ${validatedEmail.message}`);

Note from the Author or Editor:
Code samples corrected.

Sentence begins "ES6 was developed quickly...." then goes on to state that Brenden Eich admits to getting a few things wrong "the first time". The sentence is referring to the first release of JavaScript, not ECMAScript 6. Sentence should begin "JavaScript was developed quickly..."

Note from the Author or Editor:
This has been corrected.

this snippet doesn't work properly

// option 2: using "this" arg:
arr.find(p => p.id === this.id, juliet); // returns juliet object

Note from the Author or Editor:
Corrected. This only works with a regular function (not an arrow function).

Says:
console.log(z); // logs "5"

Should say:
console.log(z); // logs "3"

z was never masked or changed in the example

Note from the Author or Editor:
This has been corrected.

Says:
let arr = ["b", "c", "d"];
arr.push("e"); // returns 4; arr is now ["b", "c", "d", "e"]
arr.pop(); // returns "f"; arr is now ["b", "c", "d"]

Should say:
arr.pop(); // returns "e"; arr is now ["b", "c", "d"]

Note from the Author or Editor:
Corrected in text.

I'm not sure whether it makes a difference, but the Gulp documentation states that you should install gulp-cli, not gulp, globally:

npm install -g gulp-cli

Note from the Author or Editor:
This has been corrected.

Linux/OSX instruction says "sudo install -g gulp"; should be "sudo npm install -g gulp"

Note from the Author or Editor:
This has been corrected.

The questions to the ESLint init have changed. I have installed version 2.5.1.

The questions (and my answers) are below (I've added ** in front of questions that have changed**):

** ? How would you like to configure ESLint? Answer questions about your style
? Are you using ECMAScript 6 features? Yes
** ? Are you using ES6 modules? Yes
? Where will your code run? Browser #For some reason it showed browser whether I cose Node or browser. I couldn't get it to choose Node.
** ? Do you use CommonJS? No
? Do you use JSX? No
** ? What style of indentation do you use? Spaces
? What quotes do you use for strings? Double
? What line endings do you use? Unix
? Do you require semicolons? Yes
** ? What format do you want your config file to be in? JSON #They have added the option "Javascript" to JSON and YAML

Note from the Author or Editor:
Corrected in text.

sam3.classification.family; // "Felinae"
sam3["classification"].family; // "Felinae"
sam3.classification["family"]; // "Felinae"
sam3["classification"]["family"]; // "Felinae

"Felinae" should be 'Felidae', per the value declaration at bottom of page 47

Note from the Author or Editor:
Sharp eye, thank you Bob! This has been corrected.

“From here on out, when you install local packages, you should add either the --save or --saveDev flag"

from looking at npm documentation this should be
"--save-dev" instead of "--saveDev"

Note from the Author or Editor:
Corrected in text.

const arr4 = [
{ name: "Fred", type: "object", luckyNumbers = [5, 7, 13] },
...
];

Should be "luckyNumbers: [5, 7, 13]" with colon (:) for key : value in a object.

Note from the Author or Editor:
Corrected.

The tip states that the k words would be in their original order. However, according to the documentation on MDN sort isn't necessarily stable. Hence isn't the order of k words undefined?

Note from the Author or Editor:
After investigating, I've concluded that the reader is correct. I have not been able to find a JavaScript implementation or situation where the sort was not stable, but the specification does indeed not guarantee that. I have updated the text accordingly.

The text states that find returns null, if no element was found, but it actually returns undefined.

Note from the Author or Editor:
This has been corrected.

names.map(String.toLowerCase) results in error:

TypeError: undefined is not a function

Note from the Author or Editor:
This has been corrected.

InsurancePolicy class definition is followed by parentheses:

class InsurancePolicy() {}

which will produce the following error:

Uncaught SyntaxError: Unexpected token (

Note from the Author or Editor:
Corrected.

"... done, which becomes false after you read the last page." should use true instead of false. It currently contradicts the example of page 176.

Note from the Author or Editor:
Corrected.

Chapter 12, generators and return, p182

function* abc (){}
const it = count();

It should be:
const it = abc();

Note from the Author or Editor:
Corrected.

current version:

function fact(n) {
if(n === 1) return 1;
return n * fact(n-1);
}

mathematically correct version

function fact(n) {
if(n === 0) return 1;
return n * fact(n-1);
}

Note from the Author or Editor:
This has been corrected. I believe I originally left out the special case of 0! thinking that it would be unnecessarily confusing, but in retrospect, I see that was the wrong decision!

"Unless you are on UTC (hello, Timbuktu, Madrid, and Greenwich!),"

Madrid time zone is not UTC, is UTC+1 or UTC+2 in summer time

Note from the Author or Editor:
Corrected in text.

"const x = 3800.5;
x.toExponential(4); // "3.8005e+4";
x.toExponential(3); // "3.801e+4";
x.toExponential(2); // "3.80e+4";
x.toExponential(1); // "3.8e+4";
x.toExponential(0); // "4e+4";"

All of them should read e+3 instead of e+4

Note from the Author or Editor:
Corrected in text.

Non-capturing groups don't seem to work for the example, so that the regular expression should rather be /([A-Z])([A-Z])\2\1/g.

Note from the Author or Editor:
This has been corrected.

The note after the code listing says "The exports shorthand only works for exporting objects; if you want to export a function or some other value, you must use module.exports."

The second part of the sentence is incorrect on two counts:
* A function is an object.
* The preceding code listing shows the exports shorthand being used to export functions. When tested, the code works as expected.

The first sentence of the note should be revised along the following lines: "The exports shorthand works only for exporting functions or other objects; if you want to export some other value, you must use module.exports."

Note from the Author or Editor:
I can see how this footnote is confusingly worded, but this errata is not correct. You can certainly use the "exports" shorthand to export functions that are properties of the export object, but that is not the same as exporting a (single) function from the module; you're still exporting an object that just happens to contain function properties. As for functions being objects, that's true, but that's an implementation detail, and for practical intents and purposes objects are objects and functions are functions. I did, however, clean up the language to be more precise and clear.

object.defineProperties(object, descriptors)

Descriptor should be an object {}.

const arr = [3, 1.5, 9, 2, 5.2];

Object.defineProperties(arr, { // missing curly brace

sum: {

value: function() {

return this.reduce((a, x) => a+x);

},
enumerable: false

}, // without Parentheses

avg: {

value: function() {

return this.sum()/this.length;

},
enumerable: false

} // without Parentheses

}); // missing closing curly brace

console.log(`${arr.sum()}`); // 20.7
console.log(`${arr.avg()}`); // 4.14

Note from the Author or Editor:
Corrected.

Object.isExtensible(log2); // true

// Logs false.

Object.isExtensible(log2); // false

Note from the Author or Editor:
Corrected.

.eslintrc file => . eslintrc.js file

Note from the Author or Editor:
Corrected.

Mobi location 2869
6. Functions -- Function Arguments -- Do Arguments Make the Function?

"For example, in C, f() (no arguments) is a different function than f(x) (one argument), which is a different function than f(x, y) (two arguments)."

C does not support function overloading in the traditional sense (C11 added the _Generic keyword, which allows you to emulate function overloading with the help of the preprocessor) [1]. Suggest changing this sentence to a language that does support function overloading, such as C++ or Java, to avoid confusing new programmers.

Note from the Author or Editor:
This is a fair point; while the wording is technically correct, it does imply that if C did not include the signature, you could have two functions named f, which is not correct. I have changed the example to use C++, per the reader's suggestion.