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The 2 gets concatenated to '1', so it’s like '1' + 2 = "12" and "12" + 2 = "… : the binary form that we used above and the unary form.… The prefix form returns the new value while the postfix form returns the old value (prior to increment… So, the alert shows 1.… It’s like (a = 1 + 2), 3 + 4.

The formula for a 2-points curve: P = (1-t)P1 + tP2 For 3 control points: P = (1−t)2P1 + 2(1−t)tP2… For instance, the 3-point curve is formed by points (x,y) calculated as: x = (1−t)2x1 + 2(1−t)tx2 +… For instance, if control points are (0,0), (0.5, 1) and (1, 0), the equations become: x = (1−t)2 *… 0 + 2(1−t)t * 0.5 + t2 * 1 = (1-t)t + t2 = t y = (1−t)2 * 0 + 2(1−t)t * 1 + t2 * 0 = 2(1-t)t = –2t2 +… 2t Now as t runs from 0 to 1, the set of values (x,y) for each t forms the curve for such control points

That’s when a user clicks somewhere else or presses Tab to go to the next form field, or there are other… we generally should show errors to the user, but should not prevent their progress in filling our form… That is, when we switch elements, elements with tabindex=0 go after elements with tabindex ≥ 1.… To make an element a part of the form on par with <input>.… tabindex="-1" allows only programmatic focusing on an element.

So in the code above all alert show the same: 1.… So the output is the same as in the previous example: 1 → 2 → 4, but now with 1 second delay between… In the example above resolve(2) is called after 1 second (**).… We’ll use the fetch method to load the information about the user from the remote server.… For instance, we’d like to show a form for editing that user or something else.

String Conversion.String conversion happens when we need the string form of a value.… Explicit conversion is usually required when we read a value from a string-based source like a text form… Numeric conversion rules: Value Becomes… undefined NaN null 0 true and false 1… The conversion follows the rules: Value Becomes… undefined NaN null 0 true / false 1 / 0

know, JavaScript strings are based on Unicode: each character is represented by a byte sequence of 1-… \u{X…XXXXXX} X…XXXXXX must be a hexadecimal value of 1 to 6 bytes between 0 and 10FFFF (the highest code… That said, if we take from position 1… this, there exists a “Unicode normalization” algorithm that brings each string to the single “normal” form… , but for most practical purposes the information from this section is enough.

Sleep until a task appears, then go to 1.… The tasks form a queue, the so-called “macrotask queue” (v8 term):… Use-case 1: splitting CPU-hungry tasks.Let’s say we have a CPU-hungry task.… queued and then executes when part 1 finished, before the next part.… Go to step 1. To schedule a new macrotask: Use zero delayed setTimeout(f).

Then on the outer <form>.… So if we click on <p>, then we’ll see 3 alerts: p → div → form.… No matter where the click happened, it bubbles up to <form> and runs the handler.… runs on it. event.target is the actual element inside the form that was clicked.… the first listener): P → DIV → FORM → BODY → HTML (bubbling phase, the second listener).

-(253-1), as we mentioned earlier in the chapter Data types.… More ways to write a number.Imagine we need to write 1 billion.… -1 -1 -1.5 -2 -1 -1 -1 -1.6 -2 -1 -2 -1 These functions cover all of the possible ways to deal… It is one divided by ten 1/10, one-tenth.… A few examples: Math.random() Returns a random number from 0 to 1 (not including 1).

A number is a sequence of 1 or more digits \d.… It has a few advanced forms, let’s see examples: The exact count: {5} \d{5} denotes exactly 5 digits… So the regexp is \d{1,}:… Shorthands.There are shorthands for most used quantifiers: + Means “one or more”, the same as {1,

For instance, the Promise.all below settles after 3 seconds, and then its result is an array [1, 2, 3… For instance, here the results are [1, 2, 3]:… For example, we’d like to fetch the information about multiple users.… For instance, here the result will be 1:… For instance, here the result will be 1:

In maths, one would write xn = x * xn-1.… pow(2, 1).The process repeats: a new subcall is made at line 5, now with arguments x=2, n=1.… at line 1 } pow(2, 1) Context: { x: 2, n: 2, at line 5 } pow(2, 2) Context… pow(2, 1).… It has the result of the subcall pow(2, 1), so it also can finish the evaluation of x * pow(x, n - 1)

Starting from the index 1 it removed 1 element.… The value of -1 is returned if nothing is found.… So the function result is 1.… On the second run, sum = 1, we add the second array element (2) to it and return.… 1 the second call 1 2 3 the third call 3 3 6 the fourth call 6 4 10 the fifth call 10 5 15

BigInt.In JavaScript, the “number” type cannot safely represent integer values larger than (253-1) (that… ’s 9007199254740991), or less than -(253-1) for negatives.… store larger integers (up to 1.7976931348623157 * 10308), but outside of the safe integer range ±(253-1)… For most purposes ±(253-1) range is quite enough, but sometimes we need the entire range of really big… We can put anything in there: a variable like name or an arithmetical expression like 1 + 2 or something

When it is called like curriedSum(1), the argument is saved in the Lexical Environment, and a new wrapper… instance, we have the logging function log(date, importance, message) that formats and outputs the information… : …But also works in the curried form

For example, let’s add the default slot to our <user-card> that shows all unslotted information… All the unslotted light DOM content gets into the “Other information… Elements are appended to a slot one after another, so both unslotted pieces of information are in the… For example, here the menu item is inserted dynamically after 1 second, and the title changes after 2… After 1 second: slotchange: item triggers, when a new <li slot="item"> is added.

regexp for time.In previous articles there was a task to build a regexp for searching time in the form… First, the hours: If the first digit is 0 or 1, then the next digit can be any: [01]\d.

In this chapter we’ll cover selection in the document, as well as selection in form fields, such as &… As we can see, this phrase consists of exactly two children of <p>, with indexes 0 and 1:… imply that there may be many ranges, but again, in all browsers except Firefox, there’s at maximum 1.… Selection in form controls.Form elements, such as input and textarea provide special API for selection… In its simplest one-argument form it replaces the user selected range and removes the selection.

An errorless example: shows alert (1) and (2):… An example with an error: shows (1)… One of most widely used and supported is: stack Current call stack: a string with information about… And then enter -1 – there will be an immediate error, and the execution will take 0ms.… Environment-specific The information from this section is not a part of the core JavaScript

…And we’d like to use for..of loop on it, such as for(value of range), to get values from 1… The next() should return a value in the form {done: true/false, value:<loop value>}, where done… iterators: To make an object asynchronously iterable, it must have a method Symbol.asyncIterator (1)… Now values come with a delay of 1… allows us to retrieve commits in the same, paginated fashion: We should make a request to fetch in the form

Event constructor.Built-in event classes form a hierarchy, similar to DOM element classes.… In the second argument (object) we can add an additional property detail for any custom information that… The output order is: 1… The output order becomes: 1 → 2 → nested.

Using forms.One way to communicate with another server was to submit a <form> there.… So, it was possible to make a GET/POST request to another site, even without networking methods, as forms… , multipart/form-data or text/plain.… , multipart/form-data, text/plain.… , multipart/form-data or text/plain.

If there’s no such flag it returns only the first match in the form of an array, with the full match… part of the string before the match $' inserts a part of the string after the match $n if n is a 1-… Full information about the methods is given in the article Methods of RegExp and String. Summary.

They both call func with arguments 1,… That’s the simplest form of it: When… Append glue and this[1]. Append glue and this[2]. …Do so until this.length items are glued.… So, technically it takes this and joins this[0], this[1] …etc together.… decorator may count how many times a function was invoked and how much time it took, and expose this information

Some programming languages allow the use of negative indexes for the same purpose, like fruits[-1].… We can explicitly calculate the last element index and then access it: fruits[fruits.length - 1].… Both fruits.pop() and fruits.at(-1)… Move all elements to the left, renumber them from the index 1 to 0, from 2 to 1 and so on.… becomes "1" and [1,2] becomes "1,2".

The "for..in" loop.To walk over all keys of an object, there exists a special form of the loop… But if we run the code, we see a totally different picture: USA (1) goes first then Switzerland (41)… So we see 1, 41, 44, 49. Integer properties? What’s that?… other kinds of objects in JavaScript: Array to store ordered data collections, Date to store the information… about the date and time, Error to store the information about an error.

Working with forms will be much more convenient when we learn them.… Navigation: form and elements.Document forms are members of the special collection document.forms.… So a form references all elements, and elements reference the form.… Form elements are available as form.elements[name/index], or can use just form[name/index].… the form property.

For instance, we can set the cookie to expire in 1 day:… That site has JavaScript code that submits a form <form action="https://bank.com/pay">… The browser sends cookies every time you visit the site bank.com, even if the form was submitted from… It can submit a form there, but can’t get the data back.… The site bank.com checks for such a token in every form it receives.

On the teststand below, all mouse events are logged, and if there is more than a 1 second delay between… event.button are: Button state event.button Left button (primary) 0 Middle button (auxiliary) 1… property that’s an old non-standard way of getting a button, with possible values: event.which == 1… Modifiers: shift, alt, ctrl and meta.All mouse events include the information about pressed modifier

Tags are element nodes (or just elements) and form the tree structure: <html> is at the root, then… The text inside elements forms text nodes, labelled as #text. A text node contains only a string.… They form text nodes and become a part of the DOM.… Now the last selected element is available as $0, the previously selected is $1 etc.… Tags become element nodes and form the structure. Text becomes text nodes.

An XMLHttpRequest object travels them in the order 0 → 1… Additional calls add information to the header, don’t overwrite it.… We create it, optionally fill from a form… fields if needed, and then: xhr.open('POST', ...) – use POST method. xhr.send(formData) to submit the form… is sent with multipart/form-data encoding.

As the application grows, our own errors naturally form a hierarchy.… An error of that kind should also carry the information about the offending field.… Please note: in the line (1)… It will carry additional information about the property that’s missing.

Built-in browser autofill.Firefox, Chrome and Opera autofill forms on DOMContentLoaded.… For instance, if the page has a form with login and password, and the browser remembered the values,… We can send not only a string, but also forms and other formats, as described in the chapter Fetch, but… You can find more information in the chapter Fetch API.… The typical output: [1] initial readyState:loading [2] readyState:interactive [2] DOMContentLoaded [

The ancestors together form the chain of parents from the element to the top.… As of now, its length is 1.… If we use it instead, then both scripts output 1:

The submit event triggers when the form is submitted, it is usually used to validate the form before… The method form.submit() allows to initiate form sending from JavaScript.… We can use it to dynamically create and send our own forms to server.… Both actions lead to submit event on the form.… In the form below: Go into the text field and press Enter.

Then we can open the database with version 1 and perform the initialization in an upgradeneeded handler… suitable for users that are accessing for the first time and have no database, and also for version 1,… Let’s say: A visitor opened our site in a browser tab, with database version 1.… So there’s a tab with an open connection to DB version 1, while the second one attempts to update it… And it can’t be both version 1 and 2.

For instance: The navigator object provides background information about the browser and the operating… style rules, manipulations with them, and their binding to documents, see https://www.w3.org/TR/cssom-1/

. \', \", \` Quotes \\ Backslash \t Tab \b, \f, \v Backspace, Form Feed, Vertical Tab –… So .at(-1) means the last character, and .at(-2) is the one before it, etc.… in str, starting from the given position pos, and returns the position where the match was found or -1… For instance, the first occurrence of "id" is at position 1.… So, we should actually check for -1, like this:

str.search(regexp).The method str.search(regexp) returns the position of the first match or -1… part of the string before the match $' inserts a part of the string after the match $n if n is a 1-… Using a function gives us the ultimate replacement power, because it gets all the information

there are also common properties and methods between all of them, because all classes of DOM nodes form… It has a numeric value: elem.nodeType == 1 for element nodes, elem.nodeType == 3 for text nodes, elem.nodeType… Sometimes developers embed information or template instructions into HTML in them, like this:… The classes form a hierarchy.… It has a numeric value: 1 for elements,3 for text nodes, and a few others for other node types.

, outputting goods from a list one after another or just running the same code for each number from 1… This form… Usually, the other form is preferred: while(…) {…}.

For example, here 1+2 results in 3, while the function call hello("debugger") returns nothing… set, the execution pauses at the 4th line: Please open the informational… The information from this chapter is enough to begin debugging, but later, especially if you do a lot

For instance, the number 1 is treated as true, the number 0 as false:… A value is returned in its original form, without the conversion.

…But please note: the example above shows 1, then 2, and that’s all. It doesn’t show 3!… generator methods are exactly what for..of expects: it has a .next() method that returns values in the form… The error, thrown into the generator at line (2) leads to an exception in line (1)

In binary form, 256 is 100000000 (9 bits), but Uint8Array only provides 8 bits per value, that makes… For 257, the binary form is 100000001 (9 bits), the rightmost 8 get stored, so we’ll have 1 in the array

An exotic variable as a loop counter is especially cool if the loop body takes 1-2 pages (make it longer… cornerless The great vessel is last complete, The great note is rarified sound, The great image has no form… an outsider tries to understand the code, they’ll be surprised to see that there’s actually no information

socket.readyState property with values: 0 – “CONNECTING”: the connection has not yet been established, 1… HTML: we need a <form> to send messages and a <div> for incoming messages:… On form submission – socket.send(message) for the message.

Wrote some code, testing: f(1) works, but f(2) doesn’t work. We fix the code and now f(2) works.… But we forgot to re-test f(1). That may lead to an error. That’s very typical.… Making tests separate is useful to get more information about what’s going on, so the second variant

admin object: As you can see, when 1.… import.meta.The object import.meta contains the information… Build tools.In real-life, browser modules are rarely used in their “raw” form

Step 1.… Environment Record – an object that stores all local variables as its properties (and some other information