Merge branch 'master' of github.com:javascript-tutorial/en.javascript.info into sync-34a80e70

Author: iliakan

.github/FUNDING.yml

@@ -0,0 +1 @@
+github: iliakan

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

@@ -88,16 +88,16 @@ In older scripts, you may also find another keyword: `var` instead of `let`:
 *!*var*/!* message = 'Hello';
 ```
 
-The `var` keyword is *almost* the same as `let`. It also declares a variable, but in a slightly different, "old-school" way.
+The `var` keyword is *almost* the same as `let`. It also declares a variable but in a slightly different, "old-school" way.
 
-There are subtle differences between `let` and `var`, but they do not matter for us yet. We'll cover them in detail in the chapter <info:var>.
+There are subtle differences between `let` and `var`, but they do not matter to us yet. We'll cover them in detail in the chapter <info:var>.
 ````
 
 ## A real-life analogy
 
 We can easily grasp the concept of a "variable" if we imagine it as a "box" for data, with a uniquely-named sticker on it.
 
-For instance, the variable `message` can be imagined as a box labeled `"message"` with the value `"Hello!"` in it:
+For instance, the variable `message` can be imagined as a box labelled `"message"` with the value `"Hello!"` in it:
 
 ![](variable.svg)
 
@@ -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](https://www.scala-lang.org/) or [Erlang](https://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]
@@ -198,14 +198,14 @@ 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, Chinese logograms and so on, like this:
+It is possible to use any language, including Cyrillic letters, Chinese logograms and so on, like this:
 
 ```js
 let имя = '...';
 let 我 = '...';
 ```
 
-Technically, there is no error here. Such names are allowed, but there is an international convention to use English in variable names. Even if we're writing a small script, it may have a long life ahead. People from other countries may need to read it some time.
+Technically, there is no error here. Such names are allowed, but there is an international convention to use English in variable names. Even if we're writing a small script, it may have a long life ahead. People from other countries may need to read it sometime.
 ````
 
 ````warn header="Reserved names"
@@ -260,11 +260,11 @@ const myBirthday = '18.04.1982';
 myBirthday = '01.01.2001'; // error, can't reassign the constant!
 ```
 
-When a programmer is sure that a variable will never change, they can declare it with `const` to guarantee and clearly communicate that fact to everyone.
+When a programmer is sure that a variable will never change, they can declare it with `const` to guarantee and communicate that fact to everyone.
 
 ### Uppercase constants
 
-There is a widespread practice to use constants as aliases for difficult-to-remember values that are known prior to execution.
+There is a widespread practice to use constants as aliases for difficult-to-remember values that are known before execution.
 
 Such constants are named using capital letters and underscores.
 
@@ -289,15 +289,15 @@ Benefits:
 
 When should we use capitals for a constant and when should we name it normally? Let's make that clear.
 
-Being a "constant" just means that a variable's value never changes. But there are constants that are known prior to execution (like a hexadecimal value for red) and there are constants that are *calculated* in run-time, during the execution, but do not change after their initial assignment.
+Being a "constant" just means that a variable's value never changes. But some constants are known before execution (like a hexadecimal value for red) and some constants are *calculated* in run-time, during the execution, but do not change after their initial assignment.
 
 For instance:
 
 ```js
 const pageLoadTime = /* time taken by a webpage to load */;
 ```
 
-The value of `pageLoadTime` is not known prior to the page load, so it's named normally. But it's still a constant because it doesn't change after assignment.
+The value of `pageLoadTime` is not known before the page load, so it's named normally. But it's still a constant because it doesn't change after the assignment.
 
 In other words, capital-named constants are only used as aliases for "hard-coded" values.
 
@@ -307,18 +307,18 @@ Talking about variables, there's one more extremely important thing.
 
 A variable name should have a clean, obvious meaning, describing the data that it stores.
 
-Variable naming is one of the most important and complex skills in programming. A quick glance at variable names can reveal which code was written by a beginner versus an experienced developer.
+Variable naming is one of the most important and complex skills in programming. A glance at variable names can reveal which code was written by a beginner versus an experienced developer.
 
-In a real project, most of the time is spent modifying and extending an existing code base rather than writing something completely separate from scratch. When we return to some code after doing something else for a while, it's much easier to find information that is well-labeled. Or, in other words, when the variables have good names.
+In a real project, most of the time is spent modifying and extending an existing code base rather than writing something completely separate from scratch. When we return to some code after doing something else for a while, it's much easier to find information that is well-labelled. Or, in other words, when the variables have good names.
 
 Please spend time thinking about the right name for a variable before declaring it. Doing so will repay you handsomely.
 
 Some good-to-follow rules are:
 
 - Use human-readable names like `userName` or `shoppingCart`.
-- Stay away from abbreviations or short names like `a`, `b`, `c`, unless you really know what you're doing.
+- Stay away from abbreviations or short names like `a`, `b`, and `c`, unless you know what you're doing.
 - Make names maximally descriptive and concise. Examples of bad names are `data` and `value`. Such names say nothing. It's only okay to use them if the context of the code makes it exceptionally obvious which data or value the variable is referencing.
-- Agree on terms within your team and in your own mind. If a site visitor is called a "user" then we should name related variables `currentUser` or `newUser` instead of `currentVisitor` or `newManInTown`.
+- Agree on terms within your team and in your mind. If a site visitor is called a "user" then we should name related variables `currentUser` or `newUser` instead of `currentVisitor` or `newManInTown`.
 
 Sounds simple? Indeed it is, but creating descriptive and concise variable names in practice is not. Go for it.
 

1-js/02-first-steps/05-types/article.md

@@ -94,13 +94,6 @@ const bigInt = 1234567890123456789012345678901234567890n;
 
 As `BigInt` numbers are rarely needed, we don't cover them here, but devoted them a separate chapter <info:bigint>. Read it when you need such big numbers.
 
-
-```smart header="Compatibility issues"
-Right now, `BigInt` is supported in Firefox/Chrome/Edge/Safari, but not in IE.
-```
-
-You can check [*MDN* BigInt compatibility table](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/BigInt#Browser_compatibility) to know which versions of a browser are supported.
-
 ## String
 
 A string in JavaScript must be surrounded by quotes.
@@ -224,7 +217,7 @@ 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:
 

1-js/02-first-steps/07-type-conversions/article.md

@@ -34,7 +34,7 @@ String conversion is mostly obvious. A `false` becomes `"false"`, `null` becomes
 
 ## Numeric Conversion
 
-Numeric conversion happens in mathematical functions and expressions automatically.
+Numeric conversion in mathematical functions and expressions happens automatically.
 
 For example, when division `/` is applied to non-numbers:
 

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:
 
@@ -305,7 +306,7 @@ let n = 2;
 
 n *= 3 + 5; // right part evaluated first, same as n *= 8
 
-alert( n ); // 16  
+alert( n ); // 16
 ```
 
 ## Increment/decrement

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`:
 

1-js/02-first-steps/12-nullish-coalescing-operator/article.md

@@ -37,7 +37,7 @@ Here's the example with `user` assigned to a name:
 ```js run
 let user = "John";
 
-alert(user ?? "Anonymous"); // John (user is not null/udefined)
+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`.
@@ -76,7 +76,7 @@ alert(firstName || lastName || nickName || "Anonymous"); // Supercoder
 */!*
 ```
 
-Historically, the OR `||` operator was there first. It exists since the beginning of JavaScript, so developers were using it for such purposes for a long time.
+Historically, the OR `||` operator was there first. It's been there since the beginning of JavaScript, so developers were using it for such purposes for a long time.
 
 On the other hand, the nullish coalescing operator `??` was added to JavaScript only recently, and the reason for that was that people weren't quite happy with `||`.
 

1-js/02-first-steps/18-javascript-specials/article.md

@@ -103,13 +103,13 @@ More in: <info:variables> and <info:types>.
 
 We're using a browser as a working environment, so basic UI functions will be:
 
-[`prompt(question, [default])`](mdn:api/Window/prompt)
+[`prompt(question, [default])`](https://developer.mozilla.org/en-US/docs/Web/API/Window/prompt)
 : Ask a `question`, and return either what the visitor entered or `null` if they clicked "cancel".
 
-[`confirm(question)`](mdn:api/Window/confirm)
+[`confirm(question)`](https://developer.mozilla.org/en-US/docs/Web/API/Window/confirm)
 : Ask a `question` and suggest to choose between Ok and Cancel. The choice is returned as `true/false`.
 
-[`alert(message)`](mdn:api/Window/alert)
+[`alert(message)`](https://developer.mozilla.org/en-US/docs/Web/API/Window/alert)
 : Output a `message`.
 
 All these functions are *modal*, they pause the code execution and prevent the visitor from interacting with the page until they answer.
@@ -144,7 +144,7 @@ Assignments
 : There is a simple assignment: `a = b` and combined ones like `a *= 2`.
 
 Bitwise
-: Bitwise operators work with 32-bit integers at the lowest, bit-level: see the [docs](mdn:/JavaScript/Guide/Expressions_and_Operators#bitwise_operators) when they are needed.
+: Bitwise operators work with 32-bit integers at the lowest, bit-level: see the [docs](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Expressions_and_Operators#bitwise_operators) when they are needed.
 
 Conditional
 : The only operator with three parameters: `cond ? resultA : resultB`. If `cond` is truthy, returns `resultA`, otherwise `resultB`.

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

@@ -7,7 +7,7 @@ Teams behind JavaScript engines have their own ideas about what to implement fir
 
 So it's quite common for an engine to implement only part of the standard.
 
-A good page to see the current state of support for language features is <https://kangax.github.io/compat-table/es6/> (it's big, we have a lot to study yet).
+A good page to see the current state of support for language features is <https://compat-table.github.io/compat-table/es6/> (it's big, we have a lot to study yet).
 
 As programmers, we'd like to use most recent features. The more good stuff - the better!
 
@@ -73,7 +73,6 @@ JavaScript is a highly dynamic language. Scripts may add/modify any function, ev
 
 Two interesting polyfill libraries are:
 - [core js](https://github.com/zloirock/core-js) that supports a lot, allows to include only needed features.
-- [polyfill.io](https://polyfill.io/) service that provides a script with polyfills, depending on the features and user's browser.
 
 
 ## Summary
@@ -85,7 +84,7 @@ Just don't forget to use a transpiler (if using modern syntax or operators) and
 For example, later when you're familiar with JavaScript, you can setup a code build system based on [webpack](https://webpack.js.org/) with the [babel-loader](https://github.com/babel/babel-loader) plugin.
 
 Good resources that show the current state of support for various features:
-- <https://kangax.github.io/compat-table/es6/> - for pure JavaScript.
+- <https://compat-table.github.io/compat-table/es6/> - for pure JavaScript.
 - <https://caniuse.com/> - for browser-related functions.
 
 P.S. Google Chrome is usually the most up-to-date with language features, try it if a tutorial demo fails. Most tutorial demos work with any modern browser though.

1-js/04-object-basics/04-object-methods/8-chain-calls/task.md

@@ -4,7 +4,7 @@ importance: 2
 
 # Chaining
 
-There's a `ladder` object that allows to go up and down:
+There's a `ladder` object that allows you to go up and down:
 
 ```js
 let ladder = {
@@ -21,7 +21,7 @@ let ladder = {
 };
 ```
 
-Now, if we need to make several calls in sequence, can do it like this:
+Now, if we need to make several calls in sequence, we can do it like this:
 
 ```js
 ladder.up();
@@ -32,10 +32,10 @@ ladder.down();
 ladder.showStep(); // 0
 ```
 
-Modify the code of `up`, `down` and `showStep` to make the calls chainable, like this:
+Modify the code of `up`, `down`, and `showStep` to make the calls chainable, like this:
 
 ```js
 ladder.up().up().down().showStep().down().showStep(); // shows 1 then 0
 ```
 
-Such approach is widely used across JavaScript libraries.
+Such an approach is widely used across JavaScript libraries.