Merge branch 'master' of github.com:javascript-tutorial/en.javascript.info into sync-3a0b3f4e

Author: iliakan

1-js/01-getting-started/2-manuals-specifications/article.md

@@ -13,20 +13,15 @@ A new specification version is released every year. In-between these releases, t
 
 To read about new bleeding-edge features, including those that are "almost standard" (so-called "stage 3"), see proposals at <https://github.com/tc39/proposals>.
 
-Also, if you're in developing for the browser, then there are other specs covered in the [second part](info:browser-environment) of the tutorial.
+Also, if you're in developing for the browser, then there are other specifications covered in the [second part](info:browser-environment) of the tutorial.
 
 ## Manuals
 
-- **MDN (Mozilla) JavaScript Reference** is a manual with examples and other information. It's great to get in-depth information about individual language functions, methods etc.
+- **MDN (Mozilla) JavaScript Reference** is the main manual with examples and other information. It's great to get in-depth information about individual language functions, methods etc.
 
     One can find it at <https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference>.
 
-    Although, it's often best to use an internet search instead. Just use "MDN [term]" in the query, e.g. <https://google.com/search?q=MDN+parseInt> to search for `parseInt` function.
-
-
-- **MSDN** – Microsoft manual with a lot of information, including JavaScript (often referred to as JScript). If one needs something specific to Internet Explorer, better go there: <http://msdn.microsoft.com/>.
-
-    Also, we can use an internet search with phrases such as "RegExp MSDN" or "RegExp MSDN jscript".
+Although, it's often best to use an internet search instead. Just use "MDN [term]" in the query, e.g. <https://google.com/search?q=MDN+parseInt> to search for `parseInt` function.
 
 ## Compatibility tables
 

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

@@ -116,7 +116,7 @@ There are two types of indents:
 
     One advantage of spaces over tabs is that spaces allow more flexible configurations of indents than the tab symbol.
 
-    For instance, we can align the arguments with the opening bracket, like this:
+    For instance, we can align the parameters with the opening bracket, like this:
 
     ```js no-beautify
     show(parameters,

1-js/03-code-quality/02-coding-style/code-style.svg

@@ -14,8 +14,8 @@ Simply put, "reachable" values are those that are accessible or usable somehow.
 
     For instance:
 
-    - Local variables and parameters of the current function.
-    - Variables and parameters for other functions on the current chain of nested calls.
+    - The currently executing function, its local variables and parameters.
+    - Other functions on the current chain of nested calls, their local variables and parameters.
     - Global variables.
     - (there are some other, internal ones as well)
 

1-js/04-object-basics/03-garbage-collection/article.md

@@ -15,6 +15,11 @@ describe("calculator", function() {
     afterEach(function() {
       prompt.restore();
     });
+    
+    it('the read get two values and saves them as object properties', function () {
+      assert.equal(calculator.a, 2);
+      assert.equal(calculator.b, 3);
+    });
 
     it("the sum is 5", function() {
       assert.equal(calculator.sum(), 5);

1-js/04-object-basics/04-object-methods/7-calculator/_js.view/test.js

@@ -10,6 +10,11 @@ describe("calculator", function() {
     calculator = new Calculator();
     calculator.read();
   });
+  
+  it("the read method asks for two values using prompt and remembers them in object properties", function() {
+    assert.equal(calculator.a, 2);
+    assert.equal(calculator.b, 3);
+  });
 
   it("when 2 and 3 are entered, the sum is 5", function() {
     assert.equal(calculator.sum(), 5);

1-js/04-object-basics/06-constructor-new/2-calculator-constructor/_js.view/test.js

@@ -91,7 +91,7 @@ The syntax from this section is rarely used, skip it unless you want to know eve
 
 Inside a function, we can check whether it was called with `new` or without it, using a special `new.target` property.
 
-It is empty for regular calls and equals the function if called with `new`:
+It is undefined for regular calls and equals the function if called with `new`:
 
 ```js run
 function User() {

1-js/04-object-basics/06-constructor-new/article.md

@@ -74,12 +74,12 @@ That's why the optional chaining `?.` was added to the language. To solve this p
 
 ## Optional chaining
 
-The optional chaining `?.` stops the evaluation if the part before `?.` is `undefined` or `null` and returns that part.
+The optional chaining `?.` stops the evaluation if the value before `?.` is `undefined` or `null` and returns `undefined`.
 
 **Further in this article, for brevity, we'll be saying that something "exists" if it's not `null` and not `undefined`.**
 
 In other words, `value?.prop`:
-- is the same as `value.prop` if `value` exists,
+- works as `value.prop`, if `value` exists,
 - otherwise (when `value` is `undefined/null`) it returns `undefined`.
 
 Here's the safe way to access `user.address.street` using `?.`:
@@ -103,7 +103,7 @@ alert( user?.address.street ); // undefined
 
 Please note: the `?.` syntax makes optional the value before it, but not any further.
 
-E.g. in `user?.address.street.name` the `?.` allows `user` to be `null/undefined`, but it's all it does. Further properties are accessed in a regular way. If we want some of them to be optional, then we'll need to replace more `.` with `?.`.
+E.g. in `user?.address.street.name` the `?.` allows `user` to safely be `null/undefined` (and returns `undefined` in that case), but that's only for `user`. Further properties are accessed in a regular way. If we want some of them to be optional, then we'll need to replace more `.` with `?.`.
 
 ```warn header="Don't overuse the optional chaining"
 We should use `?.` only where it's ok that something doesn't exist.
@@ -173,18 +173,16 @@ Then `?.()` checks the left part: if the admin function exists, then it runs (th
 The `?.[]` syntax also works, if we'd like to use brackets `[]` to access properties instead of dot `.`. Similar to previous cases, it allows to safely read a property from an object that may not exist.
 
 ```js run
+let key = "firstName";
+
 let user1 = {
   firstName: "John"
 };
 
-let user2 = null; // Imagine, we couldn't authorize the user
-
-let key = "firstName";
+let user2 = null; 
 
 alert( user1?.[key] ); // John
 alert( user2?.[key] ); // undefined
-
-alert( user1?.[key]?.something?.not?.existing); // undefined
 ```
 
 Also we can use `?.` with `delete`:

1-js/04-object-basics/07-optional-chaining/article.md

@@ -109,7 +109,7 @@ There will be no conflict between our and their identifiers, because symbols are
 
 ...But if we used a string `"id"` instead of a symbol for the same purpose, then there *would* be a conflict:
 
-```js run
+```js
 let user = { name: "John" };
 
 // Our script uses "id" property

1-js/04-object-basics/08-symbol/article.md

@@ -16,21 +16,29 @@ Imagine we need to write 1 billion. The obvious way is:
 let billion = 1000000000;
 ```
 
-But in real life, we usually avoid writing a long string of zeroes as it's easy to mistype. Also, we are lazy. We will usually write something like `"1bn"` for a billion or `"7.3bn"` for 7 billion 300 million. The same is true for most large numbers.
+We also can use underscore `_` as the separator:
 
-In JavaScript, we shorten a number by appending the letter `"e"` to the number and specifying the zeroes count:
+```js
+let billion = 1_000_000_000;
+```
+
+Here the underscore `_` plays the role of the "syntactic sugar", it makes the number more readable. The JavaScript engine simply ignores `_` between digits, so it's exactly the same one billion as above.
+
+In real life though, we try to avoid writing long sequences of zeroes. We're too lazy for that. We'll try to write something like `"1bn"` for a billion or `"7.3bn"` for 7 billion 300 million. The same is true for most large numbers.
+
+In JavaScript, we can shorten a number by appending the letter `"e"` to it and specifying the zeroes count:
 
 ```js run
 let billion = 1e9;  // 1 billion, literally: 1 and 9 zeroes
 
-alert( 7.3e9 );  // 7.3 billions (7,300,000,000)
+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.
+In other words, `e` multiplies the number by `1` with the given zeroes count.
 
 ```js
-1e3 = 1 * 1000
-1.23e6 = 1.23 * 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):
@@ -125,7 +133,7 @@ There are several built-in functions for rounding:
 : Rounds up: `3.1` becomes `4`, and `-1.1` becomes `-1`.
 
 `Math.round`
-: Rounds to the nearest integer: `3.1` becomes `3`, `3.6` becomes `4` and `-1.1` becomes `-1`.
+: Rounds to the nearest integer: `3.1` becomes `3`, `3.6` becomes `4`, the middle case: `3.5` rounds up to `4` too.
 
 `Math.trunc` (not supported by Internet Explorer)
 : Removes anything after the decimal point without rounding: `3.1` becomes `3`, `-1.1` becomes `-1`.