drafts

1-js/11-async/07-microtask-queue/article.md

@@ -126,6 +126,55 @@ Naturally, `promise` shows up first, because `setTimeout` macrotask awaits in th
 
 So call have a promise chain that doesn't wait for anything, then things like `setTimeout` or event handlers can never get in the middle.
 
+
+## Unhandled rejection
+
+Remember "unhandled rejection" event from the chapter <info:promise-error-handling>?
+
+Now, with the understanding of microtasks, we can formalize it.
+
+**"Unhandled rejection" is when a promise error is not handled at the end of the microtask queue.**
+
+For instance, consider this code:
+
+```js run
+let promise = Promise.reject(new Error("Promise Failed!"));
+
+window.addEventListener('unhandledrejection', event => {
+  alert(event.reason); // Promise Failed!
+});
+```
+
+We create a rejected `promise` and do not handle the error. So we have the "unhandled rejection" event (printed in browser console too).
+
+We wouldn't have it if we added `.catch`, like this:
+
+```js run
+let promise = Promise.reject(new Error("Promise Failed!"));
+*!*
+promise.catch(err => alert('caught'));
+*/!*
+
+// no error, all quiet
+window.addEventListener('unhandledrejection', event => alert(event.reason));
+```
+
+Now let's say, we'll be catching the error, but after an extremely small delay:
+
+```js run
+let promise = Promise.reject(new Error("Promise Failed!"));
+*!*
+setTimeout(() => promise.catch(err => alert('caught')), 0);
+*/!*
+
+// Error: Promise Failed!
+window.addEventListener('unhandledrejection', event => alert(event.reason));
+```
+
+Now the unhandled rejction appears again. Why? Because `unhandledrejection` triggers when the microtask queue is complete. The engine examines promises and, if any of them is in "rejected" state, then the event is generated.
+
+In the example above `setTimeout` adds the `.catch`, and it triggers too, of course it does, but later, after the event has already occured.
+
 ## Summary
 
 - Promise handling is always asynchronous, as all promise actions pass through the internal "promise jobs" queue, also called "microtask queue" (v8 term).

6-binary/01-arraybuffer-binary-arrays/article.md

@@ -1,4 +1,4 @@
-# ArrayBuffer and views
+# ArrayBuffer, binary arrays
 
 Binary data appears when we work with arbitrary files (uploading, downloading, creation). Or when we want to do image/audio processing.
 

6-binary/02-text-decoder/article.md

@@ -1,4 +1,4 @@
-# TextDecoder, TextEncoder
+# TextDecoder and TextEncoder
 
 What if the binary data is actually a string?
 

6-binary/04-file/article.md

@@ -102,5 +102,19 @@ Reading methods `read*` do not generate events, but rather return the result, as
 That's only inside a Web Worker though, because delays and hang-ups in Web Workers are less important, they do not affect the page.
 ```
 
+## Summary
 
-It most often used to read from files, and
+`File` object inherit from `Blob`.
+
+In addition to `Blob` methods and properties, `File` objects also have `fileName` and `lastModified` properties, plus the internal ability to read from filesystem. We usually get `File` objects from user input, like `<input>` or drag'n'drop.
+
+`FileReader` objects can read from a file or a blob, in one of three formats:
+- String (`readAsText`).
+- `ArrayBuffer` (`readAsArrayBuffer`).
+- Data url, base-64 encoded (`readAsDataURL`).
+
+In many cases though, we don't have to read the file contents.
+
+We can create a blob url with `URL.createObjectURL(file)` and assign it to `<a>` or `<img>`. This way the file can be downloaded or show up as an image, as a part of canvas etc.
+
+And if we're going to send a `File` over a network, then it's also easy, as network API like `XMLHttpRequest` or `fetch` natively accepts `File` objects.

7-network/1-fetch-basics/article.md

@@ -16,39 +16,17 @@ let promise = fetch(url, [params])
 
 The browser starts the request right away and returns a `promise`.
 
-Accepting a response is usually a two-step procedure.
+Accepting a response is usually a two-stage process.
 
-**The `promise` resolves as soon as the server responded with headers.**
+**The `promise` resolves with an object of the built-in [Response](https://fetch.spec.whatwg.org/#response-class) class as soon as the server responds with headers.**
 
-So we can access the headers, we know HTTP status, whether the response is successful, but don't have the body yet.
-
-We need to wait for the response body additionally, like this:
-
-```js run async
-let response = await fetch('https://api.github.com/repos/iliakan/javascript-tutorial-en/commits');
-*!*
-let commits = await response.json();
-*/!*
-alert(commits[0].author.login);
-```
-
-Or, using pure promises:
-
-```js run
-fetch('https://api.github.com/repos/iliakan/javascript-tutorial-en/commits')
-  .then(response => response.json())
-  .then(commits => alert(commits[0].author.login));
-```
-
-A `fetch` resolves with `response` -- an object of the built-in [Response](https://fetch.spec.whatwg.org/#response-class) class.
+So we can access the headers, we know HTTP status, whether it is successful, but don't have the body yet.
 
 The main response properties are:
 - **`ok`** -- boolean, `true` if the HTTP status code is 200-299.
 - **`status`** -- HTTP status code.
 - **`headers`** -- HTTP headers, a Map-like object.
 
-## How to get headers?
-
 We can iterate over headers the same way as over a `Map`:
 
 ```js run async
@@ -67,25 +45,41 @@ if (response.ok) {
 }
 ```
 
-## How to get response?
+To get the response body, we need to use an additional method call.
 
-`Response` allows to access the body in multiple formats, using following promises:
+`Response` allows to access the body in multiple formats, using following promise-based methods:
 
 - **`json()`** -- parse as JSON object,
 - **`text()`** -- as text,
 - **`formData()`** -- as formData (form/multipart encoding),
 - **`blob()`** -- as Blob (for binary data),
-- **`arrayBuffer()`** -- as ArrayBuffer (for binary data),
-- `response.body` is a [ReadableStream](https://streams.spec.whatwg.org/#rs-class) object, it allows to read the body chunk-by-chunk.
+- **`arrayBuffer()`** -- as ArrayBuffer (for binary data)
+- additionally, `response.body` is a [ReadableStream](https://streams.spec.whatwg.org/#rs-class) object, it allows to read the body chunk-by-chunk.
 
-We already saw how to get the response as json.
+For instance, here we get the response as JSON:
 
-As text:
+```js run async
+let response = await fetch('https://api.github.com/repos/iliakan/javascript-tutorial-en/commits');
+*!*
+let commits = await response.json();
+*/!*
+alert(commits[0].author.login);
+```
+
+Or, using pure promises:
+
+```js run
+fetch('https://api.github.com/repos/iliakan/javascript-tutorial-en/commits')
+  .then(response => response.json())
+  .then(commits => alert(commits[0].author.login));
+```
+
+To get text:
 ```js
 let text = await response.text();
 ```
 
-For the binary example, let's download an image and show it:
+And for the binary example, let's fetch and show an image (see chapter [Blob](info:blob) for details about operations on blobs):
 
 ```js async run
 let response = await fetch('/article/fetch/logo-fetch.svg');
@@ -94,172 +88,22 @@ let response = await fetch('/article/fetch/logo-fetch.svg');
 let blob = await response.blob(); // download as Blob object
 */!*
 
-// create <img> with it
+// create <img> for it
 let img = document.createElement('img');
+img.style = 'position:fixed;top:10px;left:10px;width:100px';
+document.body.append(img);
+
+// show it
 img.src = URL.createObjectURL(blob);
 
-// show it for 2 seconds
-document.body.append(img);
-img.style = 'position:fixed;top:10px;left:10px;width:100px';
-setTimeout(() => img.remove(), 2000);
+setTimeout(() => { // hide after two seconds
+  img.remove();
+  URL.revokeObjectURL(img.src);
+}, 2000);
 ```
 
-## Fetch API in detail
+```warn
+Please note: we can use only one of these methods.
 
-The second argument provides a lot of flexibility to `fetch` syntax.
-
-Here's the full list of possible options with default values (alternatives commented out):
-
-```js
-let promise = fetch(url, {
-  method: "GET", // POST, PUT, DELETE, etc.
-  headers: {
-    "Content-Type": "text/plain;charset=UTF-8"
-  },
-  body: undefined // string, FormData, Blob, BufferSource, or URLSearchParams
-  referrer: "about:client", // "" for no-referrer, or an url from the current origin
-  referrerPolicy: "", // no-referrer, no-referrer-when-downgrade, same-origin...
-  mode: "cors", // same-origin, no-cors, navigate, or websocket
-  credentials: "same-origin", // omit, include
-  cache: "default", // no-store, reload, no-cache, force-cache, or only-if-cached
-  redirect: "follow", // manual, error
-  integrity: "", // a hash, like "sha256-abcdef1234567890"
-  keepalive: false, // true
-  signal: undefined, // AbortController to abort request
-  window: window // null
-})
-```
-
-
-
-
-
-## How to track progress?
-
-To track download progress, we need to use `response.body`.
-
-It's a "readable stream" - a special object that provides access chunk-by-chunk.
-
-Here's the code to do this:
-
-```js
-const reader = response.body.getReader();
-
-while(true) {
-  // done is true for the last chunk
-  // value is Uint8Array of bytes
-  const chunk = await reader.read();
-
-  if (chunk.done) {
-    break;
-  }
-
-  console.log(`Received ${chunk.value.length} bytes`)
-}
-```
-
-We do the infinite loop, while `await reader.read()` returns response chunks.
-
-A chunk has two properties:
-- **`done`** -- true when the reading is complete.
-- **`value`** -- a typed array of bytes: `Uint8Array`.
-
-The full code to get response and log the progress:
-
-```js run async
-// Step 1: start the request and obtain a reader
-let response = await fetch('https://api.github.com/repos/iliakan/javascript-tutorial-en/commits?per_page=100');
-
-const reader = response.body.getReader();
-
-// Step 2: get total length
-const contentLength = +response.headers.get('Content-Length');
-
-// Step 3: read the data
-let receivedLength = 0;
-let chunks = [];
-while(true) {
-  const {done, value} = await reader.read();
-
-  if (done) {
-    break;
-  }
-
-  chunks.push(value);
-  receivedLength += value.length;
-
-  console.log(`Received ${receivedLength} of ${contentLength}`)
-}
-
-// Step 4: join chunks into result
-let chunksAll = new Uint8Array(receivedLength); // (4.1)
-let position = 0;
-for(let chunk of chunks) {
-	chunksAll.set(chunk, position); // (4.2)
-	position += chunk.length;
-}
-
-// Step 5: decode
-let result = new TextDecoder("utf-8").decode(chunksMerged);
-let commits = JSON.parse(result);
-
-// We're done!
-alert(commits[0].author.login);
-```
-
-Let's explain that step-by-step:
-
-1. We perform `fetch` as usual, but instead of calling `response.json()`, we obtain a stream reader `response.body.getReader()`.
-
-    Please note, we can't use both these methods to read the same response. Either use a reader or a response method to get the result.
-2. Prior to reading, we can figure out the full response length by its `Content-Length` header.
-
-    It may be absent for cross-domain requests (as in the example) and, well, technically a server doesn't have to set it. But usually it's at place.
-3. Now `await reader.read()` until it's done.
-
-    We gather the `chunks` in the array. That's important, because after the response is consumed, we won't be able to "re-read" it using `response.json()` or another way (you can try, there'll be an error).
-4. At the end, we have `chunks` -- an array of `Uint8Array` byte chunks. We need to join them into a single result. Unfortunately, there's no single method that concatenates those.
-    1. We create `new Uint8Array(receivedLength)` -- a same-type array with the combined length.
-    2. Then use `.set(chunk, position)` method that copies each `chunk` at the given `position` (one by one) in the resulting array.
-5. We have the result in `chunksAll`. It's a byte array though, not a string.
-
-    To create a string, we need to interpret these bytes. The built-in `TextEncoder` does exactly that. Then we can `JSON.parse` it.
-
-    What if it were a binary file? We could make a blob of it:
-    ```js
-    let blob = new Blob([chunksAll.buffer]);
-    ```
-
-```js run async
-let response = await fetch('https://api.github.com/repos/iliakan/javascript-tutorial-en/commits?per_page=100');
-
-const contentLength = +response.headers.get('Content-Length');
-
-const reader = response.body.getReader();
-
-let receivedLength = 0;
-let chunks = [];
-while(true) {
-  const chunk = await reader.read();
-
-  if (chunk.done) {
-    console.log("done!");
-    break;
-  }
-
-  chunks.push(chunk.value);
-
-  receivedLength += chunk.value.length;
-  console.log(`${receivedLength}/${contentLength} received`)
-}
-
-let chunksMerged = new Uint8Array(receivedLength);
-let length = 0;
-for(let chunk of chunks) {
-	chunksMerged.set(chunk, length);
-	length += chunk.length;
-}
-
-let result = new TextDecoder("utf-8").decode(chunksMerged);
-console.log(JSON.parse(result));
+If we get `response.text()`, then `response.json()` won't work, as the body content has already been processed.
 ```

7-network/10-xmlhttprequest/article.md

@@ -378,7 +378,7 @@ xhr.send(json);
 
 The `.send(body)` method is pretty omnivore. It can send almost everything, including Blob and BufferSource objects.
 
-## Tracking upload progress
+## Upload progress
 
 The `progress` event only works on the downloading stage.
 
@@ -398,7 +398,7 @@ Here's the list:
 - `timeout` -- upload timed out (if `timeout` property is set).
 - `loadend` -- upload finished with either success or error.
 
-Here's an example of upload tracking:
+Example of handlers:
 
 ```js
 xhr.upload.onprogress = function(event) {
@@ -414,6 +414,36 @@ xhr.upload.onerror = function() {
 };
 ```
 
+Here's a real-life example: file upload with progress indication:
+
+```html run
+<input type="file" onchange="upload(this.files[0])">
+
+<script>
+function upload(file) {
+  let xhr = new XMLHttpRequest();
+
+  // track upload progress
+*!*
+  xhr.upload.onprogress = function(event) {
+    console.log(`Uploaded ${event.loaded} of ${event.total}`);
+  };
+*/!*
+
+  // track completion: both successful or not
+  xhr.onloadend = function() {
+    if (xhr.status == 200) {
+      console.log("success");
+    } else {
+      console.log("error " + this.status);
+    }
+  };
+
+  xhr.open("POST", "/article/xmlhttprequest/post/upload");
+  xhr.send(file);
+}
+</script>
+```
 
 ## Summary
 

7-network/10-xmlhttprequest/post.view/server.js

@@ -17,9 +17,9 @@ function accept(req, res) {
       chunks.push(data);
       length += data.length;
 
-      // Too much POST data, kill the connection!
-      if (length > 1e6) {
-        request.connection.destroy();
+      // More than 10mb, kill the connection!
+      if (length > 1e8) {
+        req.connection.destroy();
       }
     });
 
@@ -32,6 +32,9 @@ function accept(req, res) {
       } else if (req.url == '/image') {
         res.writeHead(200, { 'Content-Type': 'application/json' });
         res.end(JSON.stringify({ message: "Image saved", imageSize: length }));
+      } else if (req.url == '/upload') {
+        res.writeHead(200, { 'Content-Type': 'application/json' });
+        res.end(JSON.stringify({ message: "Upload complete", size: length }));
       } else {
         res.writeHead(404);
         res.end("Not found");

7-network/2-fetch-crossorigin/article.md

@@ -1,27 +1,16 @@
 # Cross-Origin Fetch
 
-TODO:
-Note that "Content-Length" header is not returned by default for CORS requests
-
-==
-
-Cache-Control
-Content-Language
-Content-Type
-Expires
-Last-Modified
-Pragma
-
-
 If we make a `fetch` from an arbitrary web-site, that will probably fail.
 
-Fetching from another origin (domain/port/protocol triplet) requires special headers from the remote side.
+The core concept here is *origin* -- a domain/port/protocol triplet.
 
-For instance, let's try fetching from http://google.com:
+Cross-origin requests -- those sent to another domain or protocol or port -- require special headers from the remote side.
+
+For instance, let's try fetching from `http://example.com`:
 
 ```js run async
 try {
-  await fetch('http://google.com');
+  await fetch('http://example.com');
 } catch(err) {
   alert(err); // Failed to fetch
 }
@@ -29,27 +18,55 @@ try {
 
 Fetch fails, as expected.
 
-## Safety control
+## Why?
 
-Cross-origin requests pass a special safety control, with the sole purpose to protect the internet from evil hackers.
+Cross-origin requests are subject to the special safety control with the sole purpose to protect the internet from evil hackers.
 
-Seriously. For many years cross-domain requests were simply unavailable. The internet got used to it, people got used to it.
+Seriously. Let's make a very brief historical digression.
 
-Imagine for a second that a new standard appeared, that allows any webpage to make any requests anywhere.
+For many years Javascript was unable to perform network requests.
+
+The main way to send a request to another site was an HTML `<form>` with either `POST` or `GET` method. People submitted it to `<iframe>`, just to stay on the current page.
+
+```html
+<form target="iframe" method="POST" action="http://site.com">
+  <!-- javascript could dynamically generate and submit this kind of form -->
+</form>
+
+<iframe name="iframe"></iframe>
+```
+
+So, it *was* possible to make a request. But if the submission was to another site, then the  main window was forbidden to access `<iframe>` content. Hence, it wasn't possible to get a response.
+
+2. Open another site in `<iframe>`.
+
+
+
+For many years cross-domain requests were simply unavailable. To access another
+
+The internet got used to it, people got used to it.
+
+
+Imagine that `fetch` works from anywhere.
 
 How an evil hacker could use it?
 
-They would create a page at `http://evilhacker.com`, lure a user to it, and run `fetch` from his mail server, e.g. `http://gmail.com`.
 
+They would create a page at `http://evil.com`, and when a user comes to it, then run `fetch` from his mail server, e.g. `http://gmail.com/messages`.
 
+Such a request usually sends authentication cookies, so `http://gmail.com` would recognize the user and send back the messages. Then the hacker could analyze the mail and go with online-banking, and so on.
 
-When cross-origin requests were finally implemented, safety restrictions were placed to  prevent an evil-minded person from doing anything that they couldn't do before. In such a way, that old sites are automatically protected.
+![](cors-gmail-messages.png)
 
-No script could fetch a webpage from another site (another origin, to be precise).
+How `gmail.com` and other sites protect users from such hacks now?
 
-That becomes really important, as you remember about cookies. Any request brings cookies by default, so being able to
+That's simple -- when a request is made from they add an additional secret value to all requests.
+The protection is quite simple.
+How `gmail.com`
 
- can't access the content of a page from another site.
+Right, because o
+
+Because of cross-origin restrictions such a hack is impossible. They prevent an evil-minded person from doing anything that they couldn't do before.
 
 
 

7-network/5-fetch-progress/article.md

@@ -1,41 +1,96 @@
 
-# Fetch API
+# Fetch: Track download progress
 
-The second argument provides a lot of flexibility to `fetch` syntax.
+To track download progress, we need to use `response.body`.
 
-Here's the full list of possible options with default values (alternatives commented out):
+It's a "readable stream" - a special object that provides access chunk-by-chunk.
+
+Here's the code to do this:
 
 ```js
-let promise = fetch(url, {
-  method: "GET", // POST, PUT, DELETE, etc.
-  headers: {
-    "Content-Type": "text/plain;charset=UTF-8"
-  },
-  body: undefined // string, FormData, Blob, BufferSource, or URLSearchParams
-  referrer: "about:client", // "" for no-referrer, or an url from the current origin
-  referrerPolicy: "", // no-referrer, no-referrer-when-downgrade, same-origin...
-  mode: "cors", // same-origin, no-cors, navigate, or websocket
-  credentials: "same-origin", // omit, include
-  cache: "default", // no-store, reload, no-cache, force-cache, or only-if-cached
-  redirect: "follow", // manual, error
-  integrity: "", // a hash, like "sha256-abcdef1234567890"
-  keepalive: false, // true
-  signal: undefined, // AbortController to abort request
-  window: window // null
-})
+const reader = response.body.getReader();
+
+while(true) {
+  // done is true for the last chunk
+  // value is Uint8Array of bytes
+  const chunk = await reader.read();
+
+  if (chunk.done) {
+    break;
+  }
+
+  console.log(`Received ${chunk.value.length} bytes`)
+}
 ```
 
-Not so long list actually, but quite a lot of capabilities.
+We do the infinite loop, while `await reader.read()` returns response chunks.
 
-Let's explore the options one-by-one with examples.
+A chunk has two properties:
+- **`done`** -- true when the reading is complete.
+- **`value`** -- a typed array of bytes: `Uint8Array`.
 
-## method, headers, body
+The full code to get response and log the progress:
 
-These are the most widely used fields.
+```js run async
+// Step 1: start the request and obtain a reader
+let response = await fetch('https://api.github.com/repos/iliakan/javascript-tutorial-en/commits?per_page=100');
 
-- **`method`** -- HTTP-method, e.g. POST,
-- **`headers`** -- an object with HTTP headers,
-- **`body`** -- a string, or:
-  - FormData object, to submit `form/multipart`
-  - Blob/BufferSource to send binary data
-  - URLSearchParams, to submit `x-www-form-urlencoded`
+const reader = response.body.getReader();
+
+// Step 2: get total length
+const contentLength = +response.headers.get('Content-Length');
+
+// Step 3: read the data
+let receivedLength = 0;
+let chunks = [];
+while(true) {
+  const {done, value} = await reader.read();
+
+  if (done) {
+    break;
+  }
+
+  chunks.push(value);
+  receivedLength += value.length;
+
+  console.log(`Received ${receivedLength} of ${contentLength}`)
+}
+
+// Step 4: join chunks into result
+let chunksAll = new Uint8Array(receivedLength); // (4.1)
+let position = 0;
+for(let chunk of chunks) {
+	chunksAll.set(chunk, position); // (4.2)
+	position += chunk.length;
+}
+
+// Step 5: decode into a string
+let result = new TextDecoder("utf-8").decode(chunksAll);
+let commits = JSON.parse(result);
+
+// We're done!
+alert(commits[0].author.login);
+```
+
+Let's explain that step-by-step:
+
+1. We perform `fetch` as usual, but instead of calling `response.json()`, we obtain a stream reader `response.body.getReader()`.
+
+    Please note, we can't use both these methods to read the same response. Either use a reader or a response method to get the result.
+2. Prior to reading, we can figure out the full response length by its `Content-Length` header.
+
+    It may be absent for cross-domain requests (as in the example) and, well, technically a server doesn't have to set it. But usually it's at place.
+3. Now `await reader.read()` until it's done.
+
+    We gather the `chunks` in the array. That's important, because after the response is consumed, we won't be able to "re-read" it using `response.json()` or another way (you can try, there'll be an error).
+4. At the end, we have `chunks` -- an array of `Uint8Array` byte chunks. We need to join them into a single result. Unfortunately, there's no single method that concatenates those.
+    1. We create `new Uint8Array(receivedLength)` -- a same-type array with the combined length.
+    2. Then use `.set(chunk, position)` method that copies each `chunk` at the given `position` (one by one) in the resulting array.
+5. We have the result in `chunksAll`. It's a byte array though, not a string.
+
+    To create a string, we need to interpret these bytes. The built-in `TextEncoder` does exactly that. Then we can `JSON.parse` it.
+
+What if we need binary content instead of JSON? That's even simpler. Instead of steps 4 and 5, we could make a blob of all chunks:
+```js
+let blob = new Blob(chunks);
+```

7-network/5-fetch-progress/post.view/index.html

@@ -0,0 +1,36 @@
+<!doctype html>
+<script>
+(async () {
+	
+	const response = await fetch('long.txt');
+	const reader = response.body.getReader();
+
+	const contentLength = +response.headers.get('Content-Length');
+	let receivedLength = 0;
+	let chunks = [];
+	while(true) {
+		const chunk = await reader.read();
+
+		if (chunk.done) {
+			console.log("done!");
+			break;
+		}
+
+		chunks.push(chunk.value);
+		receivedLength += chunk.value.length;
+		console.log(`${receivedLength}/${contentLength} received`)
+	}
+
+
+	let chunksMerged = new Uint8Array(receivedLength);
+	let length = 0;
+	for(let chunk of chunks) {
+		chunksMerged.set(chunk, length);
+		length += chunk.length;
+	}
+
+	let result = new TextDecoder("utf-8").decode(chunksMerged);
+	console.log(result);
+})();
+
+</script>

7-network/5-fetch-progress/post.view/server.js

@@ -0,0 +1,55 @@
+let http = require('http');
+let url = require('url');
+let querystring = require('querystring');
+let static = require('node-static');
+let file = new static.Server('.', {
+  cache: 0
+});
+
+
+function accept(req, res) {
+
+  if (req.method == 'POST') {
+    let chunks = [];
+    let length = 0;
+
+    req.on('data', function (data) {
+      chunks.push(data);
+      length += data.length;
+
+      // Too much POST data, kill the connection!
+      if (length > 1e6) {
+        request.connection.destroy();
+      }
+    });
+
+    req.on('end', function() {
+      // let post = JSON.parse(chunks.join(''));
+
+      if (req.url == '/user') {
+        res.writeHead(200, { 'Content-Type': 'application/json' });
+        res.end(JSON.stringify({ message: 'User saved' }));
+      } else if (req.url == '/image') {
+        res.writeHead(200, { 'Content-Type': 'application/json' });
+        res.end(JSON.stringify({ message: "Image saved", imageSize: length }));
+      } else {
+        res.writeHead(404);
+        res.end("Not found");
+      }
+    });
+
+
+  } else {
+    file.serve(req, res);
+  }
+
+}
+
+
+// ------ запустить сервер -------
+
+if (!module.parent) {
+  http.createServer(accept).listen(8080);
+} else {
+  exports.accept = accept;
+}

7-network/6-url/article.md

@@ -1,4 +1,96 @@
 
-# Fetch
+# URL objects
 
-[codetabs src="progress"]
+The built-in [URL](https://url.spec.whatwg.org/#api) class provides a convenient interface for creating and parsing URLs.
+
+We don't have to use it at all. There are no networking methods that require exactly an `URL` object, strings are good enough. But sometimes it can be really helpful.
+
+## Creating an URL
+
+The syntax to create a new URL object:
+
+```js
+new URL(url, [base])
+```
+
+- **`url`** -- the text url
+- **`base`** -- an optional base for the `url`
+
+The `URL` object immediately allows us to access its components, so it's a nice way to parse the url, e.g.:
+
+```js run
+let url = new URL('https://javascript.info/url');
+
+alert(url.protocol); // https:
+alert(url.host);     // javascript.info
+alert(url.pathname); // /url
+```
+
+Here's the cheatsheet:
+
+![](url-object.png)
+
+- `href` is the full url, same as `url.toString()`
+- `protocol` ends with the colon character `:`
+- `search` starts with the question mark `?`
+- `hash` ends with the hash character `#`
+- there are also `user` and `password` properties if HTTP authentication is present.
+
+We can also use `URL` to create relative urls, using the second argument:
+
+```js run
+let url = new URL('profile/admin', 'https://javascript.info');
+
+alert(url); // https://javascript.info/profile/admin
+
+url = new URL('tester', url); // go to 'tester' relative to current url path
+
+alert(url); // https://javascript.info/profile/tester
+```
+
+```smart header="We can use `URL` everywhere instead of a string"
+We can use an `URL` object in `fetch` or `XMLHttpRequest`, almost everywhere where a string url is expected.
+
+In the vast majority of methods it's automatically converted to a string.
+```
+
+## SearchParams
+
+Let's say we want to create an url with given search params, for instance, `https://google.com/search?query=value`.
+
+They must be correctly encoded.
+
+In very old browsers, before `URL` apparead, we'd use built-in functions `encodeURIComponent/decodeURIComponent`.
+
+Now, there's no need: `url.searchParams` is an object of type [URLSearchParams](https://url.spec.whatwg.org/#urlsearchparams).
+
+It provides convenient methods for search parameters:
+
+- **`append(name, value)`** -- add the parameter,
+- **`delete(name)`** -- remove the parameter,
+- **`get(name)`** -- get the parameter,
+- **`getAll(name)`** -- get all parameters with that name,
+- **`has(name)`** -- check for the existance of the parameter,
+- **`set(name, value)`** -- set/replace the parameter,
+- **`sort()`** -- sort parameters by name, rarely needed,
+- ...and also iterable, similar to `Map`.
+
+So, `URL` object also provides an easy way to operate on url parameters.
+
+For example:
+
+```js run
+let url = new URL('https://google.com/search');
+url.searchParams.set('query', 'test me!');
+
+alert(url); // https://google.com/search?query=test+me%21
+
+url.searchParams.set('tbs', 'qdr:y'); // add param for date range: past year
+
+alert(url); // https://google.com/search?query=test+me%21&tbs=qdr%3Ay
+
+// iterate over search parameters (decoded)
+for(let [name, value] of url.searchParams) {
+  alert(`${name}=${value}`); // query=test me!, then tbs=qdr:y
+}
+```