javascript-tutorial · leviding · Jan 8, 2023 · Jan 8, 2023
diff --git a/1-js/01-getting-started/1-intro/article.md b/1-js/01-getting-started/1-intro/article.md
@@ -35,15 +35,15 @@ The terms above are good to remember because they are used in developer articles
 Engines are complicated. But the basics are easy.
 
 1. The engine (embedded if it's a browser) reads ("parses") the script.
-2. Then it converts ("compiles") the script to the machine language.
+2. Then it converts ("compiles") the script to machine code.
 3. And then the machine code runs, pretty fast.
 
 The engine applies optimizations at each step of the process. It even watches the compiled script as it runs, analyzes the data that flows through it, and further optimizes the machine code based on that knowledge.
 ```
 
 ## What can in-browser JavaScript do?
 
-Modern JavaScript is a "safe" programming language. It does not provide low-level access to memory or CPU, because it was initially created for browsers which do not require it.
+Modern JavaScript is a "safe" programming language. It does not provide low-level access to memory or the CPU, because it was initially created for browsers which do not require it.
 
 JavaScript's capabilities greatly depend on the environment it's running in. For instance, [Node.js](https://wikipedia.org/wiki/Node.js) supports functions that allow JavaScript to read/write arbitrary files, perform network requests, etc.
 
@@ -59,25 +59,25 @@ 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 a 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 to protect the 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:
 
 - JavaScript on a webpage may not read/write arbitrary files on the hard disk, copy them or execute programs. It has no direct access to OS functions.
 
     Modern browsers allow it to work with files, but the access is limited and only provided if the user does certain actions, like "dropping" a file into a browser window or selecting it via an `<input>` tag.
 
-    There are ways to interact with camera/microphone and other devices, but they require a user's explicit permission. So a JavaScript-enabled page may not sneakily enable a web-camera, observe the surroundings and send the information to the [NSA](https://en.wikipedia.org/wiki/National_Security_Agency).
-- Different tabs/windows generally do not know about each other. Sometimes they do, for example when one window uses JavaScript to open the other one. But even in this case, JavaScript from one page may not access the other if they come from different sites (from a different domain, protocol or port).
+    There are ways to interact with the camera/microphone and other devices, but they require a user's explicit permission. So a JavaScript-enabled page may not sneakily enable a web-camera, observe the surroundings and send the information to the [NSA](https://en.wikipedia.org/wiki/National_Security_Agency).
+- Different tabs/windows generally do not know about each other. Sometimes they do, for example when one window uses JavaScript to open the other one. But even in this case, JavaScript from one page may not access the other page if they come from different sites (from a different domain, protocol or port).
 
-    This is called the "Same Origin Policy". To work around that, *both pages* must agree for data exchange and contain a special JavaScript code that handles it. We'll cover that in the tutorial.
+    This is called the "Same Origin Policy". To work around that, *both pages* must agree for data exchange and must contain special JavaScript code that handles it. We'll cover that in the tutorial.
 
-    This limitation is, again, for the user's safety. A page from `http://anysite.com` which a user has opened must not be able to access another browser tab with the URL `http://gmail.com` and steal information from there.
+    This limitation is, again, for the user's safety. A page from `http://anysite.com` which a user has opened must not be able to access another browser tab with the URL `http://gmail.com`, for example, and steal information from there.
 - JavaScript can easily communicate over the net to the server where the current page came from. But its ability to receive data from other sites/domains is crippled. Though possible, it requires explicit agreement (expressed in HTTP headers) from the remote side. Once again, that's a safety limitation.
 
 ![](limitations.svg)
 
-Such limits do not exist if JavaScript is used outside of the browser, for example on a server. Modern browsers also allow plugin/extensions which may ask for extended permissions.
+Such limitations do not exist if JavaScript is used outside of the browser, for example on a server. Modern browsers also allow plugins/extensions which may ask for extended permissions.
 
 ## What makes JavaScript unique?
 
@@ -92,28 +92,28 @@ JavaScript is the only browser technology that combines these three things.
 
 That's what makes JavaScript unique. That's why it's the most widespread tool for creating browser interfaces.
 
-That said, JavaScript also allows to create servers, mobile applications, etc.
+That said, JavaScript can be used to create servers, mobile applications, etc.
 
 ## Languages "over" JavaScript
 
 The syntax of JavaScript does not suit everyone's needs. Different people want different features.
 
 That's to be expected, because projects and requirements are different for everyone.
 
-So recently a plethora of new languages appeared, which are *transpiled* (converted) to JavaScript before they run in the browser.
+So, recently a plethora of new languages appeared, which are *transpiled* (converted) to JavaScript before they run in the browser.
 
 Modern tools make the transpilation very fast and transparent, actually allowing developers to code in another language and auto-converting it "under the hood".
 
 Examples of such languages:
 
-- [CoffeeScript](https://coffeescript.org/) is a "syntactic sugar" for JavaScript. It introduces shorter syntax, allowing us to write clearer and more precise code. Usually, Ruby devs like it.
+- [CoffeeScript](https://coffeescript.org/) is "syntactic sugar" for JavaScript. It introduces shorter syntax, allowing us to write clearer and more precise code. Usually, Ruby devs like it.
 - [TypeScript](https://www.typescriptlang.org/) is concentrated on adding "strict data typing" to simplify the development and support of complex systems. It is developed by Microsoft.
 - [Flow](https://flow.org/) also adds data typing, but in a different way. Developed by Facebook.
 - [Dart](https://www.dartlang.org/) is a standalone language that has its own engine that runs in non-browser environments (like mobile apps), but also can be transpiled to JavaScript. Developed by Google.
 - [Brython](https://brython.info/) is a Python transpiler to JavaScript that enables the writing of applications in pure Python without JavaScript.
 - [Kotlin](https://kotlinlang.org/docs/reference/js-overview.html) is a modern, concise and safe programming language that can target the browser or Node.
 
-There are more. Of course, even if we use one of transpiled languages, we should also know JavaScript to really understand what we're doing.
+There are more. Of course, even if we use one of these transpiled languages, we should also know JavaScript to really understand what we're doing.
 
 ## Summary
 

diff --git a/1-js/01-getting-started/3-code-editors/article.md b/1-js/01-getting-started/3-code-editors/article.md
@@ -29,11 +29,11 @@ The main difference between a "lightweight editor" and an "IDE" is that an IDE w
 
 In practice, lightweight editors may have a lot of plugins including directory-level syntax analyzers and autocompleters, so there's no strict border between a lightweight editor and an IDE.
 
-The following options deserve your attention:
+There are many options, for instance:
 
-- [Sublime Text](http://www.sublimetext.com) (cross-platform, shareware).
+- [Sublime Text](https://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.
+- [Vim](https://www.vim.org/) and [Emacs](https://www.gnu.org/software/emacs/) are also cool if you know how to use them.
 
 ## Let's not argue
 
@@ -42,3 +42,8 @@ The editors in the lists above are those that either I or my friends whom I cons
 There are other great editors in our big world. Please choose the one you like the most.
 
 The choice of an editor, like any other tool, is individual and depends on your projects, habits, and personal preferences.
+
+The author's personal opinion:
+
+- I'd use [Visual Studio Code](https://code.visualstudio.com/) if I develop mostly frontend.
+- Otherwise, if it's mostly another language/platform and partially frontend, then consider other editors, such as XCode (Mac), Visual Studio (Windows) or Jetbrains family (Webstorm, PHPStorm, RubyMine etc, depending on the language).
diff --git a/1-js/02-first-steps/04-variables/3-uppercast-constant/task.md b/1-js/02-first-steps/04-variables/3-uppercast-constant/task.md
@@ -12,13 +12,14 @@ const birthday = '18.04.1982';
 const age = someCode(birthday);
 ```
 
-Here we have a constant `birthday` date and the `age` is calculated from `birthday` with the help of some code (it is not provided for shortness, and because details don't matter here).
+Here we have a constant `birthday` for the date, and also the `age` constant.
+
+The `age` is calculated from `birthday` using `someCode()`, which means a function call that we didn't explain yet (we will soon!), but the details don't matter here, the point is that `age` is calculated somehow based on the `birthday`.
 
 Would it be right to use upper case for `birthday`? For `age`? Or even for both?
 
 ```js
-const BIRTHDAY = '18.04.1982'; // make uppercase?
+const BIRTHDAY = '18.04.1982'; // make birthday uppercase?
 
-const AGE = someCode(BIRTHDAY); // make uppercase?
+const AGE = someCode(BIRTHDAY); // make age uppercase?
 ```
-
diff --git a/1-js/02-first-steps/04-variables/article.md b/1-js/02-first-steps/04-variables/article.md
@@ -151,11 +151,11 @@ So, we should declare a variable once and then refer to it without `let`.
 ````
 
 ```smart header="Functional languages"
-It's interesting to note that there exist [functional](https://en.wikipedia.org/wiki/Functional_programming) programming languages, like [Scala](http://www.scala-lang.org/) or [Erlang](http://www.erlang.org/) that forbid changing variable values.
+It's interesting to note that there exist so-called [pure functional](https://en.wikipedia.org/wiki/Purely_functional_programming) programming languages, such as [Haskell](https://en.wikipedia.org/wiki/Haskell), that forbid changing variable values.
 
 In such languages, once the value is stored "in the box", it's there forever. If we need to store something else, the language forces us to create a new box (declare a new variable). We can't reuse the old one.
 
-Though it may seem a little odd at first sight, these languages are quite capable of serious development. More than that, there are areas like parallel computations where this limitation confers certain benefits. Studying such a language (even if you're not planning to use it soon) is recommended to broaden the mind.
+Though it may seem a little odd at first sight, these languages are quite capable of serious development. More than that, there are areas like parallel computations where this limitation confers certain benefits.
 ```
 
 ## Variable naming [#variable-naming]
@@ -198,7 +198,7 @@ Variables named `apple` and `APPLE` are two different variables.
 ```
 
 ````smart header="Non-Latin letters are allowed, but not recommended"
-It is possible to use any language, including cyrillic letters or even hieroglyphs, like this:
+It is possible to use any language, including cyrillic letters, Chinese logograms and so on, like this:
 
 ```js
 let имя = '...';

diff --git a/1-js/02-first-steps/05-types/article.md b/1-js/02-first-steps/05-types/article.md
@@ -224,7 +224,7 @@ The `symbol` type is used to create unique identifiers for objects. We have to m
 
 ## The typeof operator [#type-typeof]
 
-The `typeof` operator returns the type of the argument. It's useful when we want to process values of different types differently or just want to do a quick check.
+The `typeof` operator returns the type of the operand. It's useful when we want to process values of different types differently or just want to do a quick check.
 
 A call to `typeof x` returns a string with the type name:
 

diff --git a/1-js/02-first-steps/07-type-conversions/article.md b/1-js/02-first-steps/07-type-conversions/article.md
@@ -70,7 +70,7 @@ Numeric conversion rules:
 |`undefined`|`NaN`|
 |`null`|`0`|
 |<code>true&nbsp;and&nbsp;false</code> | `1` and `0` |
-| `string` | Whitespaces from the start and end are removed. If the remaining string is empty, the result is `0`. Otherwise, the number is "read" from the string. An error gives `NaN`. |
+| `string` | Whitespaces (includes spaces, tabs `\t`, newlines `\n` etc.) from the start and end are removed. If the remaining string is empty, the result is `0`. Otherwise, the number is "read" from the string. An error gives `NaN`. |
 
 Examples:
 
@@ -130,7 +130,7 @@ The conversion follows the rules:
 |`undefined`|`NaN`|
 |`null`|`0`|
 |<code>true&nbsp;/&nbsp;false</code> | `1 / 0` |
-| `string` | The string is read "as is", whitespaces from both sides are ignored. An empty string becomes `0`. An error gives `NaN`. |
+| `string` | The string is read "as is", whitespaces (includes spaces, tabs `\t`, newlines `\n` etc.) from both sides are ignored. An empty string becomes `0`. An error gives `NaN`. |
 
 **`Boolean Conversion`** -- Occurs in logical operations. Can be performed with `Boolean(value)`.
 

diff --git a/1-js/02-first-steps/08-operators/3-primitive-conversions-questions/solution.md b/1-js/02-first-steps/08-operators/3-primitive-conversions-questions/solution.md
@@ -22,4 +22,4 @@ undefined + 1 = NaN // (6)
 4. The subtraction always converts to numbers, so it makes `"  -9  "` a number `-9` (ignoring spaces around it).
 5. `null` becomes `0` after the numeric conversion.
 6. `undefined` becomes `NaN` after the numeric conversion.
-7. Space characters, are trimmed off string start and end when a string is converted to a number. Here the whole string consists of space characters, such as `\t`, `\n` and a "regular" space between them. So, similarly to an empty string, it becomes `0`.
+7. Space characters are trimmed off string start and end when a string is converted to a number. Here the whole string consists of space characters, such as `\t`, `\n` and a "regular" space between them. So, similarly to an empty string, it becomes `0`.
diff --git a/1-js/02-first-steps/08-operators/article.md b/1-js/02-first-steps/08-operators/article.md
@@ -50,8 +50,9 @@ The result of `a % b` is the [remainder](https://en.wikipedia.org/wiki/Remainder
 For instance:
 
 ```js run
-alert( 5 % 2 ); // 1, a remainder of 5 divided by 2
-alert( 8 % 3 ); // 2, a remainder of 8 divided by 3
+alert( 5 % 2 ); // 1, the remainder of 5 divided by 2
+alert( 8 % 3 ); // 2, the remainder of 8 divided by 3
+alert( 8 % 4 ); // 0, the remainder of 8 divided by 4
 ```
 
 ### Exponentiation **
@@ -68,7 +69,7 @@ alert( 2 ** 3 ); // 2³ = 8
 alert( 2 ** 4 ); // 2⁴ = 16
 ```
 
-Just like in maths, the exponentiation operator is defined for non-integer numbers as well. 
+Just like in maths, the exponentiation operator is defined for non-integer numbers as well.
 
 For example, a square root is an exponentiation by ½:
 
@@ -80,7 +81,7 @@ alert( 8 ** (1/3) ); // 2 (power of 1/3 is the same as a cubic root)
 
 ## String concatenation with binary +
 
-Let's meet features of JavaScript operators that are beyond school arithmetics.
+Let's meet the features of JavaScript operators that are beyond school arithmetics.
 
 Usually, the plus operator `+` sums numbers.
 
@@ -194,18 +195,18 @@ Here's an extract from the [precedence table](https://developer.mozilla.org/en-U
 | Precedence | Name | Sign |
 |------------|------|------|
 | ... | ... | ... |
-| 15 | unary plus | `+` |
-| 15 | unary negation | `-` |
-| 14 | exponentiation | `**` |
-| 13 | multiplication | `*` |
-| 13 | division | `/` |
-| 12 | addition | `+` |
-| 12 | subtraction | `-` |
+| 14 | unary plus | `+` |
+| 14 | unary negation | `-` |
+| 13 | exponentiation | `**` |
+| 12 | multiplication | `*` |
+| 12 | division | `/` |
+| 11 | addition | `+` |
+| 11 | subtraction | `-` |
 | ... | ... | ... |
 | 2 | assignment | `=` |
 | ... | ... | ... |
 
-As we can see, the "unary plus" has a priority of `15` which is higher than the `12` of "addition" (binary plus). That's why, in the expression `"+apples + +oranges"`, unary pluses work before the addition.
+As we can see, the "unary plus" has a priority of `14` which is higher than the `11` of "addition" (binary plus). That's why, in the expression `"+apples + +oranges"`, unary pluses work before the addition.
 
 ## Assignment
 
@@ -303,9 +304,9 @@ Such operators have the same precedence as a normal assignment, so they run afte
 ```js run
 let n = 2;
 
-n *= 3 + 5;
+n *= 3 + 5; // right part evaluated first, same as n *= 8
 
-alert( n ); // 16  (right part evaluated first, same as n *= 8)
+alert( n ); // 16
 ```
 
 ## Increment/decrement

diff --git a/1-js/02-first-steps/10-ifelse/article.md b/1-js/02-first-steps/10-ifelse/article.md
@@ -68,7 +68,7 @@ if (cond) {
 
 ## The "else" clause
 
-The `if` statement may contain an optional "else" block. It executes when the condition is falsy.
+The `if` statement may contain an optional `else` block. It executes when the condition is falsy.
 
 For example:
 ```js run
@@ -181,9 +181,9 @@ alert( message );
 It may be difficult at first to grasp what's going on. But after a closer look, we can see that it's just an ordinary sequence of tests:
 
 1. The first question mark checks whether `age < 3`.
-2. If true -- it returns `'Hi, baby!'`. Otherwise, it continues to the expression after the colon '":"', checking `age < 18`.
-3. If that's true -- it returns `'Hello!'`. Otherwise, it continues to the expression after the next colon '":"', checking `age < 100`.
-4. If that's true -- it returns `'Greetings!'`. Otherwise, it continues to the expression after the last colon '":"', returning `'What an unusual age!'`.
+2. If true -- it returns `'Hi, baby!'`. Otherwise, it continues to the expression after the colon ":", checking `age < 18`.
+3. If that's true -- it returns `'Hello!'`. Otherwise, it continues to the expression after the next colon ":", checking `age < 100`.
+4. If that's true -- it returns `'Greetings!'`. Otherwise, it continues to the expression after the last colon ":", returning `'What an unusual age!'`.
 
 Here's how this looks using `if..else`:
 

diff --git a/1-js/02-first-steps/12-nullish-coalescing-operator/article.md b/1-js/02-first-steps/12-nullish-coalescing-operator/article.md
@@ -29,15 +29,15 @@ For example, here we show `user` if its value isn't `null/undefined`, otherwise
 ```js run
 let user;
 
-alert(user ?? "Anonymous"); // Anonymous (user not defined)
+alert(user ?? "Anonymous"); // Anonymous (user is undefined)
 ```
 
 Here's the example with `user` assigned to a name:
 
 ```js run
 let user = "John";
 
-alert(user ?? "Anonymous"); // John (user defined)
+alert(user ?? "Anonymous"); // John (user is not null/undefined)
 ```
 
 We can also use a sequence of `??` to select the first value from a list that isn't `null/undefined`.
@@ -106,7 +106,7 @@ In practice, the zero height is often a valid value, that shouldn't be replaced
 
 ## Precedence
 
-The precedence of the `??` operator is the same as `||`. They both equal `4` in the [MDN table](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Operator_Precedence#Table).
+The precedence of the `??` operator is the same as `||`. They both equal `3` in the [MDN table](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Operator_Precedence#Table).
 
 That means that, just like `||`, the nullish coalescing operator `??` is evaluated before `=` and `?`, but after most other operations, such as `+`, `*`.