Merge pull request #49 from javascript-tutorial/sync-291b5c05

Sync with upstream @ 291b5c0

Author: niemenjoki

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

@@ -24,11 +24,11 @@ Selaimeen on upotettu moottori, jota kutsutaan joskus "JavaScript-virtuaalikonee
 
 Eri moottoreilla on omia kutsumanimiä. Esimerkiksi:
 
-- [V8](https://fi.wikipedia.org/wiki/V8_(JavaScript-moottori)) -- Chromessa ja Operassa.
+- [V8](https://fi.wikipedia.org/wiki/V8_(JavaScript-moottori)) -- Chromessa, Operassa ja Edgessä.
 - [SpiderMonkey](https://en.wikipedia.org/wiki/SpiderMonkey) -- Firefoxissa.
 - ...Lisäksi on muitakin kutsumanimiä kuten "Chakra" IE:lle, "JavaScriptCore", "Nitro" ja "SquirrelFish" Safarille, jne.
 
-Yllä luetellut termit on hyvä muistaa, koska niitä käytetään internetin sovelluskehitykseen liittyvissä artikkeleissa. Me tulemme myös käyttämään niitä. Jos esimerkiksi "V8 tukee toimintoa X", se todennäköisesti toimii Chromessa ja Operassa.
+Yllä luetellut termit on hyvä muistaa, koska niitä käytetään internetin sovelluskehitykseen liittyvissä artikkeleissa. Me tulemme myös käyttämään niitä. Jos esimerkiksi "V8 tukee toimintoa X", se todennäköisesti toimii Chromessa, Operassa ja Edgessä.
 
 ```smart header="Miten moottorit toimivat?"
 
@@ -59,7 +59,7 @@ Selaimessa JavaScript voi esimerkiksi:
 
 ## Mitä JavaScript EI VOI tehdä selaimessa?
 
-JavaScriptin kyvyt selaimessa on rajoitettu käyttäjän turvallisuuden vuoksi. Tavoitteena on estää pahaa nettisivua pääsemästä käsiksi yksityisiin tietoihin tai vahingoittamasta käyttäjän tietoja.
+JavaScriptin kykyjä selaimessa on rajoitettu käyttäjän turvallisuuden vuoksi. Tavoitteena on estää pahaa nettisivua pääsemästä käsiksi yksityisiin tietoihin tai vahingoittamasta käyttäjän tietoja.
 
 Esimerkkejä tällaisista rajoituksista ovat:
 
@@ -117,6 +117,6 @@ Lisääkin esimerkkejä löytyy. Silti, vaikka käytämme jotain muunnettavaa ki
 
 ## Yhteenveto
 
-- JavaScript suunniteltiin alunperin vain selaimeen, mutta sitä käytetään nykyisin myös monissa muissa ympäristöissä.
+- JavaScript suunniteltiin alunperin vain selaimessa käytettäväksi kieleksi, mutta sitä käytetään nykyisin myös monissa muissa ympäristöissä.
 - JavaScriptillä on nykyisin uniikki asema laajimmin käytettynä selainkielenä, joka integroituu täysin HTML:ään ja CSS:ään.
 - Monet JavaScriptiksi "muunnettavat" kielet tuovat mukanaan tiettyjä toimintoja. On suositeltavaa tutustua niihin, ainakin lyhyesti, kun JavaScript on hallussa.

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

@@ -31,11 +31,18 @@ Käytännössä kevyihin editoreihin voi olla saatavilla monia lisäosia mukaan
 
 Seuraavat vaihtoehdot ansaitsevat huomiosi:
 
+<<<<<<< HEAD
 - [Atom](https://atom.io/) (järjestelmäriippumaton, ilmainen).
 - [Visual Studio Code](https://code.visualstudio.com/) (järjestelmäriippumaton, ilmainen).
 - [Sublime Text](http://www.sublimetext.com) (järjestelmäriippumaton, shareware).
 - [Notepad++](https://notepad-plus-plus.org/) (Windows, ilmainen).
 - [Vim](http://www.vim.org/) ja [Emacs](https://www.gnu.org/software/emacs/) ovat myös siistejä, jos tiedät, miten niitä käytetään.
+=======
+- [Atom](https://atom.io/) (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.
+>>>>>>> 291b5c05b99452cf8a0d32bd32426926dbcc0ce0
 
 ## Ei riidellä
 

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

@@ -73,7 +73,11 @@ Skriptitiedostot liitetään HTML:ään `src` (suom. lähde) attribuutilla:
 <script src="/polku/tiedostoon/script.js"></script>
 ```
 
+<<<<<<< HEAD
 Yllä, `/polku/tiedostoon/script.js` tarkoittaa absoluuttista tiedostopolkua skriptiin sivuston juuresta (root). Polun voi kirjoittaa myös nykyisen sivun suhteen. Esimerkiksi `src="script.js"` tarkoittaisi tiedostoa nimeltä `"script.js"` nykyisessä kansiossa.
+=======
+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.
+>>>>>>> 291b5c05b99452cf8a0d32bd32426926dbcc0ce0
 
 Voimme kirjoittaa myös koko URL-osoitteen. Esimerkiksi:
 

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

@@ -46,13 +46,15 @@ Besides regular numbers, there are so-called "special numeric values" which also
     alert( "not a number" / 2 ); // NaN, such division is erroneous
     ```
 
-    `NaN` is sticky. Any further operation on `NaN` returns `NaN`:
+    `NaN` is sticky. Any further mathematical operation on `NaN` returns `NaN`:
 
     ```js run
-    alert( "not a number" / 2 + 5 ); // NaN
+    alert( NaN + 1 ); // NaN
+    alert( 3 * NaN ); // NaN
+    alert( "not a number" / 2 - 1 ); // NaN
     ```
 
-    So, if there's a `NaN` somewhere in a mathematical expression, it propagates to the whole result.
+    So, if there's a `NaN` somewhere in a mathematical expression, it propagates to the whole result (there's only one exception to that: `NaN ** 0` is `1`).
 
 ```smart header="Mathematical operations are safe"
 Doing maths is "safe" in JavaScript. We can do anything: divide by zero, treat non-numeric strings as numbers, etc.
@@ -213,14 +215,7 @@ The `symbol` type is used to create unique identifiers for objects. We have to m
 
 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.
 
-It supports two forms of syntax:
-
-1. As an operator: `typeof x`.
-2. As a function: `typeof(x)`.
-
-In other words, it works with parentheses or without them. The result is the same.
-
-The call to `typeof x` returns a string with the type name:
+A call to `typeof x` returns a string with the type name:
 
 ```js
 typeof undefined // "undefined"
@@ -251,9 +246,19 @@ typeof alert // "function"  (3)
 The last three lines may need additional explanation:
 
 1. `Math` is a built-in object that provides mathematical operations. We will learn it in the chapter <info:number>. Here, it serves just as an example of an object.
-2. The result of `typeof null` is `"object"`. That's an officially recognized error in `typeof` behavior, coming from the early days of JavaScript and kept for compatibility. Definitely, `null` is not an object. It is a special value with a separate type of its own.
+2. The result of `typeof null` is `"object"`. That's an officially recognized error in `typeof`, coming from very early days of JavaScript and kept for compatibility. Definitely, `null` is not an object. It is a special value with a separate type of its own. The behavior of `typeof` is wrong here.
 3. The result of `typeof alert` is `"function"`, because `alert` is a function. We'll study functions in the next chapters where we'll also see that there's no special "function" type in JavaScript. Functions belong to the object type. But `typeof` treats them differently, returning `"function"`. That also comes from the early days of JavaScript. Technically, such behavior isn't correct, but can be convenient in practice.
 
+```smart header="The `typeof(x)` syntax"
+You may also come across another syntax: `typeof(x)`. It's the same as `typeof x`.
+
+To put it clear: `typeof` is an operator, not a function. The parentheses here aren't a part of `typeof`. It's the kind of parentheses used for mathematical grouping.
+
+Usually, such parentheses contain a mathematical expression, such as `(2 + 2)`, but here they contain only one argument `(x)`. Syntactically, they allow to avoid a space between the `typeof` operator and its argument, and some people like it.
+
+Some people prefer `typeof(x)`, although the `typeof x` syntax is much more common.
+```
+
 ## Summary
 
 There are 8 basic data types in JavaScript.
@@ -269,7 +274,7 @@ There are 8 basic data types in JavaScript.
 
 The `typeof` operator allows us to see which type is stored in a variable.
 
-- Two forms: `typeof x` or `typeof(x)`.
+- Usually used as `typeof x`, but `typeof(x)` is also possible.
 - Returns a string with the name of the type, like `"string"`.
 - For `null` returns `"object"` -- this is an error in the language, it's not actually an object.
 

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

@@ -7,7 +7,7 @@ For example, `alert` automatically converts any value to a string to show it. Ma
 There are also cases when we need to explicitly convert a value to the expected type.
 
 ```smart header="Not talking about objects yet"
-In this chapter, we won't cover objects. For now we'll just be talking about primitives.
+In this chapter, we won't cover objects. For now, we'll just be talking about primitives.
 
 Later, after we learn about objects, in the chapter <info:object-toprimitive> we'll see how objects fit in.
 ```

1-js/02-first-steps/08-operators/article.md

@@ -194,22 +194,22 @@ Here's an extract from the [precedence table](https://developer.mozilla.org/en-U
 | Precedence | Name | Sign |
 |------------|------|------|
 | ... | ... | ... |
-| 17 | unary plus | `+` |
-| 17 | unary negation | `-` |
-| 16 | exponentiation | `**` |
-| 15 | multiplication | `*` |
-| 15 | division | `/` |
-| 13 | addition | `+` |
-| 13 | subtraction | `-` |
+| 15 | unary plus | `+` |
+| 15 | unary negation | `-` |
+| 14 | exponentiation | `**` |
+| 13 | multiplication | `*` |
+| 13 | division | `/` |
+| 12 | addition | `+` |
+| 12 | subtraction | `-` |
 | ... | ... | ... |
-| 3 | assignment | `=` |
+| 2 | assignment | `=` |
 | ... | ... | ... |
 
-As we can see, the "unary plus" has a priority of `17` which is higher than the `13` 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 `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.
 
 ## Assignment
 
-Let's note that an assignment `=` is also an operator. It is listed in the precedence table with the very low priority of `3`.
+Let's note that an assignment `=` is also an operator. It is listed in the precedence table with the very low priority of `2`.
 
 That's why, when we assign a variable, like `x = 2 * 2 + 1`, the calculations are done first and then the `=` is evaluated, storing the result in `x`.
 
@@ -437,7 +437,7 @@ The list of operators:
 - RIGHT SHIFT ( `>>` )
 - ZERO-FILL RIGHT SHIFT ( `>>>` )
 
-These operators are used very rarely, when we need to fiddle with numbers on the very lowest (bitwise) level. We won't need these operators any time soon, as web development has little use of them, but in some special areas, such as cryptography, they are useful. You can read the [Bitwise Operators](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Expressions_and_Operators#Bitwise) chapter on MDN when a need arises.
+These operators are used very rarely, when we need to fiddle with numbers on the very lowest (bitwise) level. We won't need these operators any time soon, as web development has little use of them, but in some special areas, such as cryptography, they are useful. You can read the [Bitwise Operators](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Expressions_and_Operators#bitwise_operators) chapter on MDN when a need arises.
 
 ## Comma
 

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/12-nullish-coalescing-operator/article.md

@@ -4,7 +4,7 @@
 
 The nullish coalescing operator is written as two question marks `??`.
 
-As it treats `null` and `undefined` similarly, we'll use a special term here, in this article. We'll say that an expression is "defined" when it's neither `null` nor `undefined`.
+As it treats `null` and `undefined` similarly, we'll use a special term here, in this article. For brevity, we'll say that a value is "defined" when it's neither `null` nor `undefined`.
 
 The result of `a ?? b` is:
 - if `a` is defined, then `a`,
@@ -22,9 +22,9 @@ result = (a !== null && a !== undefined) ? a : b;
 
 Now it should be absolutely clear what `??` does. Let's see where it helps.
 
-The common use case for `??` is to provide a default value for a potentially undefined variable.
+The common use case for `??` is to provide a default value.
 
-For example, here we show `user` if defined, otherwise `Anonymous`:
+For example, here we show `user` if its value isn't `null/undefined`, otherwise `Anonymous`:
 
 ```js run
 let user;
@@ -42,9 +42,9 @@ alert(user ?? "Anonymous"); // John (user defined)
 
 We can also use a sequence of `??` to select the first value from a list that isn't `null/undefined`.
 
-Let's say we have a user's data in variables `firstName`, `lastName` or `nickName`. All of them may be not defined, if the user decided not to enter a value.
+Let's say we have a user's data in variables `firstName`, `lastName` or `nickName`. All of them may be not defined, if the user decided not to fill in the corresponding values.
 
-We'd like to display the user name using one of these variables, or show "Anonymous" if all of them aren't defined.
+We'd like to display the user name using one of these variables, or show "Anonymous" if all of them are `null/undefined`.
 
 Let's use the `??` operator for that:
 
@@ -106,11 +106,11 @@ In practice, the zero height is often a valid value, that shouldn't be replaced
 
 ## Precedence
 
-The precedence of the `??` operator is about the same as `||`, just a bit lower. It equals `5` in the [MDN table](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Operator_Precedence#Table), while `||` is `6`.
+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).
 
 That means that, just like `||`, the nullish coalescing operator `??` is evaluated before `=` and `?`, but after most other operations, such as `+`, `*`.
 
-So if we'd like to choose a value with `??` in an expression with other operators, consider adding parentheses:
+So we may need to add parentheses in expressions like this:
 
 ```js run
 let height = null;
@@ -128,7 +128,7 @@ Otherwise, if we omit parentheses, then as `*` has the higher precedence than `?
 // without parentheses
 let area = height ?? 100 * width ?? 50;
 
-// ...works the same as this (probably not what we want):
+// ...works this way (not what we want):
 let area = height ?? (100 * width) ?? 50;
 ```
 

1-js/02-first-steps/15-function-basics/1-if-else-required/solution.md

@@ -1 +1,3 @@
-No difference.
+No difference!
+
+In both cases, `return confirm('Did parents allow you?')` executes exactly when the `if` condition is falsy.