Sync with upstream @ a8291557

.gitignore

@@ -21,3 +21,4 @@ sftp-config.json
 Thumbs.db
 
 
+/svgs

1-js/01-getting-started/1-intro/article.md

@@ -24,11 +24,11 @@ The browser has an embedded engine sometimes called a "JavaScript virtual machin
 
 Different engines have different "codenames". For example:
 
-- [V8](https://en.wikipedia.org/wiki/V8_(JavaScript_engine)) -- in Chrome and Opera.
+- [V8](https://en.wikipedia.org/wiki/V8_(JavaScript_engine)) -- in Chrome, Opera and Edge.
 - [SpiderMonkey](https://en.wikipedia.org/wiki/SpiderMonkey) -- in Firefox.
 - ...There are other codenames like "Chakra" for IE, "JavaScriptCore", "Nitro" and "SquirrelFish" for Safari, etc.
 
-The terms above are good to remember because they are used in developer articles on the internet. We'll use them too. For instance, if "a feature X is supported by V8", then it probably works in Chrome and Opera.
+The terms above are good to remember because they are used in developer articles on the internet. We'll use them too. For instance, if "a feature X is supported by V8", then it probably works in Chrome, Opera and Edge.
 
 ```smart header="How do engines work?"
 
@@ -59,7 +59,7 @@ For instance, in-browser JavaScript is able to:
 
 ## What CAN'T in-browser JavaScript do?
 
-JavaScript's abilities in the browser are limited for the sake of the user's safety. The aim is to prevent an evil webpage from accessing private information or harming the user's data.
+JavaScript's abilities in the browser are limited for the sake of a user's safety. The aim is to prevent an evil webpage from accessing private information or harming the user's data.
 
 Examples of such restrictions include:
 
@@ -86,7 +86,7 @@ There are at least *three* great things about JavaScript:
 ```compare
 + Full integration with HTML/CSS.
 + Simple things are done simply.
-+ Support by all major browsers and enabled by default.
++ Supported by all major browsers and enabled by default.
 ```
 JavaScript is the only browser technology that combines these three things.
 
@@ -118,5 +118,5 @@ There are more. Of course, even if we use one of transpiled languages, we should
 ## Summary
 
 - JavaScript was initially created as a browser-only language, but it is now used in many other environments as well.
-- Today, JavaScript has a unique position as the most widely-adopted browser language with full integration in HTML/CSS.
+- Today, JavaScript has a unique position as the most widely-adopted browser language, fully integrated with HTML/CSS.
 - There are many languages that get "transpiled" to JavaScript and provide certain features. It is recommended to take a look at them, at least briefly, after mastering JavaScript.

1-js/01-getting-started/3-code-editors/article.md

@@ -32,7 +32,6 @@ In practice, lightweight editors may have a lot of plugins including directory-l
 The following options deserve your attention:
 
 - [Atom](https://atom.io/) (cross-platform, free).
-- [Visual Studio Code](https://code.visualstudio.com/) (cross-platform, free).
 - [Sublime Text](http://www.sublimetext.com) (cross-platform, shareware).
 - [Notepad++](https://notepad-plus-plus.org/) (Windows, free).
 - [Vim](http://www.vim.org/) and [Emacs](https://www.gnu.org/software/emacs/) are also cool if you know how to use them.

1-js/02-first-steps/01-hello-world/article.md

@@ -73,7 +73,7 @@ Script files are attached to HTML with the `src` attribute:
 <script src="/path/to/script.js"></script>
 ```
 
-Here, `/path/to/script.js` is an absolute path to the script from the site root. One can also provide a relative path from the current page. For instance, `src="script.js"` would mean a file `"script.js"` in the current folder.
+Here, `/path/to/script.js` is an absolute path to the script from the site root. One can also provide a relative path from the current page. For instance, `src="script.js"`, just like `src="./script.js"`, would mean a file `"script.js"` in the current folder.
 
 We can give a full URL as well. For instance:
 

1-js/02-first-steps/04-variables/article.md

@@ -24,7 +24,7 @@ Now, we can put some data into it by using the assignment operator `=`:
 let message;
 
 *!*
-message = 'Hello'; // store the string
+message = 'Hello'; // store the string 'Hello' in the variable named message
 */!*
 ```
 

1-js/02-first-steps/09-comparison/article.md

@@ -7,7 +7,7 @@ In JavaScript they are written like this:
 - Greater/less than: <code>a &gt; b</code>, <code>a &lt; b</code>.
 - Greater/less than or equals: <code>a &gt;= b</code>, <code>a &lt;= b</code>.
 - Equals: `a == b`, please note the double equality sign `==` means the equality test, while a single one `a = b` means an assignment.
-- Not equals. In maths the notation is <code>&ne;</code>, but in JavaScript it's written as <code>a != b</code>.
+- Not equals: In maths the notation is <code>&ne;</code>, but in JavaScript it's written as <code>a != b</code>.
 
 In this article we'll learn more about different types of comparisons, how JavaScript makes them, including important peculiarities.
 

1-js/02-first-steps/11-logical-operators/article.md

@@ -123,7 +123,7 @@ This leads to some interesting usage compared to a "pure, classical, boolean-onl
 
     It means that `||` processes its arguments until the first truthy value is reached, and then the value is returned immediately, without even touching the other argument.
 
-    That importance of this feature becomes obvious if an operand isn't just a value, but an expression with a side effect, such as a variable assignment or a function call.
+    The importance of this feature becomes obvious if an operand isn't just a value, but an expression with a side effect, such as a variable assignment or a function call.
 
     In the example below, only the second message is printed:
 

1-js/02-first-steps/13-while-for/article.md

@@ -106,7 +106,7 @@ Let's examine the `for` statement part-by-part:
 
 | part  |          |                                                                            |
 |-------|----------|----------------------------------------------------------------------------|
-| begin | `i = 0`    | Executes once upon entering the loop.                                      |
+| begin | `let i = 0`    | Executes once upon entering the loop.                                      |
 | condition | `i < 3`| Checked before every loop iteration. If false, the loop stops.              |
 | body | `alert(i)`| Runs again and again while the condition is truthy.                         |
 | step| `i++`      | Executes after the body on each iteration. |
@@ -377,7 +377,7 @@ label: {
 }
 ```
 
-...Although, 99.9% of the time `break` used is inside loops, as we've seen in the examples above.
+...Although, 99.9% of the time `break` is used inside loops, as we've seen in the examples above.
 
 A `continue` is only possible from inside a loop.
 ````

1-js/02-first-steps/15-function-basics/article.md

@@ -181,7 +181,7 @@ In other words, to put these terms straight:
 
 We declare functions listing their parameters, then call them passing arguments.
 
-In the example above, one might say: "the function `sayMessage` is declared with two parameters, then called with two arguments: `from` and `"Hello"`".
+In the example above, one might say: "the function `showMessage` is declared with two parameters, then called with two arguments: `from` and `"Hello"`".
 
 
 ## Default values
@@ -247,7 +247,7 @@ function showMessage(text) {
 showMessage(); // empty message
 ```
 
-...Or we could use the `??` operator:
+...Or we could use the `||` operator:
 
 ```js
 function showMessage(text) {

1-js/03-code-quality/02-coding-style/article.md

@@ -301,11 +301,11 @@ The great thing about them is that style-checking can also find some bugs, like
 
 Here are some well-known linting tools:
 
-- [JSLint](http://www.jslint.com/) -- one of the first linters.
-- [JSHint](http://www.jshint.com/) -- more settings than JSLint.
-- [ESLint](http://eslint.org/) -- probably the newest one.
+- [JSLint](https://www.jslint.com/) -- one of the first linters.
+- [JSHint](https://jshint.com/) -- more settings than JSLint.
+- [ESLint](https://eslint.org/) -- probably the newest one.
 
-All of them can do the job. The author uses [ESLint](http://eslint.org/).
+All of them can do the job. The author uses [ESLint](https://eslint.org/).
 
 Most linters are integrated with many popular editors: just enable the plugin in the editor and configure the style.
 
@@ -335,7 +335,7 @@ Here's an example of an `.eslintrc` file:
 
 Here the directive `"extends"` denotes that the configuration is based on the "eslint:recommended" set of settings. After that, we specify our own.
 
-It is also possible to download style rule sets from the web and extend them instead. See <http://eslint.org/docs/user-guide/getting-started> for more details about installation.
+It is also possible to download style rule sets from the web and extend them instead. See <https://eslint.org/docs/user-guide/getting-started> for more details about installation.
 
 Also certain IDEs have built-in linting, which is convenient but not as customizable as ESLint.
 

1-js/03-code-quality/06-polyfills/article.md

@@ -22,7 +22,7 @@ Here, in this chapter, our purpose is to get the gist of how they work, and thei
 
 ## Transpilers
 
-A [transpiler](https://en.wikipedia.org/wiki/Source-to-source_compiler) is a special piece of software that can parse ("read and understand") modern code, and rewrite it using older syntax constructs, so that the result would be the same.
+A [transpiler](https://en.wikipedia.org/wiki/Source-to-source_compiler) is a special piece of software that translates source code to another source code. It can parse ("read and understand") modern code and rewrite it using older syntax constructs, so that it'll also work in outdated engines.
 
 E.g. JavaScript before year 2020 didn't have the "nullish coalescing operator" `??`. So, if a visitor uses an outdated browser, it may fail to understand the code like `height = height ?? 100`.
 

1-js/04-object-basics/02-object-copy/article.md

@@ -133,7 +133,7 @@ clone.name = "Pete"; // changed the data in it
 alert( user.name ); // still John in the original object
 ```
 
-Also we can use the method [Object.assign](mdn:js/Object/assign) for that.
+Also we can use the method [Object.assign](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/assign) for that.
 
 The syntax is:
 

1-js/04-object-basics/06-constructor-new/1-two-functions-one-object/task.md

@@ -4,7 +4,7 @@ importance: 2
 
 # Two functions – one object
 
-Is it possible to create functions `A` and `B` such as `new A()==new B()`?
+Is it possible to create functions `A` and `B` so that `new A() == new B()`?
 
 ```js no-beautify
 function A() { ... }

1-js/04-object-basics/09-object-toprimitive/article.md

@@ -9,7 +9,7 @@ In case of such operations, objects are auto-converted to primitives, and then t
 
 That's an important limitation, as the result of `obj1 + obj2` can't be another object!
 
-E.g. we can't make objects representing vectors or matrices (or archievements or whatever), add them and expect a "summed" object as the result. Such architectural feats are automatically "off the board".
+E.g. we can't make objects representing vectors or matrices (or achievements or whatever), add them and expect a "summed" object as the result. Such architectural feats are automatically "off the board".
 
 So, because we can't do much here, there's no maths with objects in real projects. When it happens, it's usually because of a coding mistake.
 
@@ -133,7 +133,7 @@ As we can see from the code, `user` becomes a self-descriptive string or a money
 
 If there's no `Symbol.toPrimitive` then JavaScript tries to find methods `toString` and `valueOf`:
 
-- For the "string" hint: `toString`, and if it doesn't exist, then `valueOf` (so `toString` has the priority for stirng conversions).
+- For the "string" hint: `toString`, and if it doesn't exist, then `valueOf` (so `toString` has the priority for string conversions).
 - For other hints: `valueOf`, and if it doesn't exist, then `toString` (so `valueOf` has the priority for maths).
 
 Methods `toString` and `valueOf` come from ancient times. They are not symbols (symbols did not exist that long ago), but rather "regular" string-named methods. They provide an alternative "old-style" way to implement the conversion.
@@ -274,4 +274,4 @@ The conversion algorithm is:
 
 In practice, it's often enough to implement only `obj.toString()` as a "catch-all" method for string conversions that should return a "human-readable" representation of an object, for logging or debugging purposes.  
 
-As for math operations, JavaScript doesn't provide a way to "override" them using methods, so real life projects rarely use them on objects.
+As for math operations, JavaScript doesn't provide a way to "override" them using methods, so real life projects rarely use them on objects.

1-js/05-data-types/01-primitives-methods/article.md

@@ -48,7 +48,7 @@ The solution looks a little bit awkward, but here it is:
 2. The language allows access to methods and properties of strings, numbers, booleans and symbols.
 3. In order for that to work, a special "object wrapper" that provides the extra functionality is created, and then is destroyed.
 
-The "object wrappers" are different for each primitive type and are called: `String`, `Number`, `Boolean` and `Symbol`. Thus, they provide different sets of methods.
+The "object wrappers" are different for each primitive type and are called: `String`, `Number`, `Boolean`, `Symbol` and `BigInt`. Thus, they provide different sets of methods.
 
 For instance, there exists a string method [str.toUpperCase()](https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Global_Objects/String/toUpperCase) that returns a capitalized `str`.
 

1-js/05-data-types/02-number/article.md

@@ -4,7 +4,7 @@ In modern JavaScript, there are two types of numbers:
 
 1. Regular numbers in JavaScript are stored in 64-bit format [IEEE-754](https://en.wikipedia.org/wiki/IEEE_754-2008_revision), also known as "double precision floating point numbers". These are numbers that we're using most of the time, and we'll talk about them in this chapter.
 
-2. BigInt numbers, to represent integers of arbitrary length. They are sometimes needed, because a regular number can't exceed <code>2<sup>53</sup></code> or be less than <code>-2<sup>53</sup></code>. As bigints are used in few special areas, we devote them a special chapter <info:bigint>.
+2. BigInt numbers, to represent integers of arbitrary length. They are sometimes needed, because a regular number can't safely exceed <code>2<sup>53</sup></code> or be less than <code>-2<sup>53</sup></code>. As bigints are used in few special areas, we devote them a special chapter <info:bigint>.
 
 So here we'll talk about regular numbers. Let's expand our knowledge of them.
 
@@ -37,8 +37,8 @@ alert( 7.3e9 );  // 7.3 billions (same as 7300000000 or 7_300_000_000)
 In other words, `e` multiplies the number by `1` with the given zeroes count.
 
 ```js
-1e3 = 1 * 1000 // e3 means *1000
-1.23e6 = 1.23 * 1000000 // e6 means *1000000
+1e3 === 1 * 1000; // e3 means *1000
+1.23e6 === 1.23 * 1000000; // e6 means *1000000
 ```
 
 Now let's write something very small. Say, 1 microsecond (one millionth of a second):
@@ -53,16 +53,16 @@ Just like before, using `"e"` can help. If we'd like to avoid writing the zeroes
 let ms = 1e-6; // six zeroes to the left from 1
 ```
 
-If we count the zeroes in `0.000001`, there are 6 of them. So naturally it's `1e-6`.  
+If we count the zeroes in `0.000001`, there are 6 of them. So naturally it's `1e-6`.
 
 In other words, a negative number after `"e"` means a division by 1 with the given number of zeroes:
 
 ```js
 // -3 divides by 1 with 3 zeroes
-1e-3 = 1 / 1000 (=0.001)
+1e-3 === 1 / 1000; // 0.001
 
 // -6 divides by 1 with 6 zeroes
-1.23e-6 = 1.23 / 1000000 (=0.00000123)
+1.23e-6 === 1.23 / 1000000; // 0.00000123
 ```
 
 ### Hex, binary and octal numbers
@@ -118,6 +118,7 @@ Please note that two dots in `123456..toString(36)` is not a typo. If we want to
 If we placed a single dot: `123456.toString(36)`, then there would be an error, because JavaScript syntax implies the decimal part after the first dot. And if we place one more dot, then JavaScript knows that the decimal part is empty and now goes the method.
 
 Also could write `(123456).toString(36)`.
+
 ```
 
 ## Rounding
@@ -328,7 +329,7 @@ let num = +prompt("Enter a number", '');
 alert( isFinite(num) );
 ```
 
-Please note that an empty or a space-only string is treated as `0` in all numeric functions including `isFinite`.  
+Please note that an empty or a space-only string is treated as `0` in all numeric functions including `isFinite`.
 
 ```smart header="Compare with `Object.is`"
 

1-js/05-data-types/03-string/article.md

@@ -81,7 +81,7 @@ Here's the full list:
 | Character | Description |
 |-----------|-------------|
 |`\n`|New line|
-|`\r`|Carriage return: not used alone. Windows text files use a combination of two characters `\r\n` to represent a line break. |
+|`\r`|In Windows text files a combination of two characters `\r\n` represents a new break, while on non-Windows OS it's just `\n`. That's for historical reasons, most Windows software also understands `\n`. |
 |`\'`, `\"`|Quotes|
 |`\\`|Backslash|
 |`\t`|Tab|

1-js/05-data-types/05-array-methods/12-reduce-object/task.md

@@ -4,7 +4,7 @@ importance: 4
 
 # Create keyed object from array
 
-Let's say we received an array of users in the form `{id:..., name:..., age... }`.
+Let's say we received an array of users in the form `{id:..., name:..., age:... }`.
 
 Create a function `groupById(arr)` that creates an object from it, with `id` as the key, and array items as values.
 

1-js/05-data-types/09-keys-values-entries/article.md

@@ -77,7 +77,7 @@ Objects lack many methods that exist for arrays, e.g. `map`, `filter` and others
 If we'd like to apply them, then we can use `Object.entries` followed by `Object.fromEntries`:
 
 1. Use `Object.entries(obj)` to get an array of key/value pairs from `obj`.
-2. Use array methods on that array, e.g. `map`.
+2. Use array methods on that array, e.g. `map`, to transform these key/value pairs.
 3. Use `Object.fromEntries(array)` on the resulting array to turn it back into an object.
 
 For example, we have an object with prices, and would like to double them:
@@ -91,12 +91,13 @@ let prices = {
 
 *!*
 let doublePrices = Object.fromEntries(
-  // convert to array, map, and then fromEntries gives back the object
-  Object.entries(prices).map(([key, value]) => [key, value * 2])
+  // convert prices to array, map each key/value pair into another pair
+  // and then fromEntries gives back the object
+  Object.entries(prices).map(entry => [entry[0], entry[1] * 2])
 );
 */!*
 
 alert(doublePrices.meat); // 8
-```   
+```
 
-It may look difficult at first sight, but becomes easy to understand after you use it once or twice. We can make powerful chains of transforms this way. 
+It may look difficult at first sight, but becomes easy to understand after you use it once or twice. We can make powerful chains of transforms this way.

1-js/06-advanced-functions/01-recursion/05-output-single-linked-list-reverse/solution.md

@@ -33,7 +33,7 @@ printReverseList(list);
 
 # Using a loop
 
-The loop variant is also a little bit more complicated then the direct output.
+The loop variant is also a little bit more complicated than the direct output.
 
 There is no way to get the last value in our `list`. We also can't "go back".
 

1-js/06-advanced-functions/03-closure/9-sort-by-field/_js.view/test.js

@@ -23,7 +23,7 @@ describe("byField", function(){
       { name: "John", age: 20, surname: "Johnson"},
     ];
     let ageSortedAnswer = users.sort(byField("age"));
-    assert.deepEqual(ageSortedKey, ageSortedKey);
+    assert.deepEqual(ageSortedKey, ageSortedAnswer);
   });
 
   it("sorts users by surname", function(){

1-js/06-advanced-functions/04-var/article.md

@@ -4,7 +4,7 @@
 ```smart header="This article is for understanding old scripts"
 The information in this article is useful for understanding old scripts.
 
-That's not how we write a new code.
+That's not how we write new code.
 ```
 
 In the very first chapter about [variables](info:variables), we mentioned three ways of variable declaration:

1-js/06-advanced-functions/10-bind/article.md

@@ -187,8 +187,8 @@ let user = {
 
 let say = user.say.bind(user);
 
-say("Hello"); // Hello, John ("Hello" argument is passed to say)
-say("Bye"); // Bye, John ("Bye" is passed to say)
+say("Hello"); // Hello, John! ("Hello" argument is passed to say)
+say("Bye"); // Bye, John! ("Bye" is passed to say)
 ```
 
 ````smart header="Convenience method: `bindAll`"