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So if we want to track any input into an <input> field, then keyboard events are not enough.… There’s another event named input to track changes of an <input> field, by any means.… We’ll cover it later in the chapter Events: change, input, cut, copy, paste.… In the past, keyboard events were sometimes used to track user input in form fields.… We have input and change events to handle any input (covered later in the chapter Events: change, input

For text inputs that means that the event occurs when it loses focus.… : input.The input event triggers every time after a value is modified by the user.… On the other hand, input event doesn’t trigger on keyboard input and other actions that do not involve… Can’t prevent anything in oninput The input event occurs after the value is modified.… For text inputs triggers on focus loss. input For text inputs on every change.

In this chapter we’ll get into more details about mouse events and their properties.… Click the button below and you’ll see the events. Try double-click too.… On the teststand below, all mouse events are logged, and if there is more than a 1 second delay between… We usually don’t use it for click and contextmenu events, because the former happens only on left-click… On the other hand, mousedown and mouseup handlers may need event.button, because these events trigger

Keyboard events: keydown and keyup – when a keyboard key is pressed and released.… on an element, e.g. on an <input>.… When an event happens, the browser creates an event object, puts details into it and passes it as an… Many of them depend on the event type: keyboard events have one set of properties, pointer events – another… We’ll learn more about events in general and about different types of events in the next chapters.

Events focus/blur.The focus event is called on focusing, and blur – when the element loses the focus.… Let’s use them for validation of an input field.… If we enter something into the input and then try to use Tab or click away from the <input>, then… elements without tabindex (e.g. a regular <input>).… >, the focus event triggers on that input only.

Many sites were hacked this way, including Twitter, Facebook, Paypal and other sites.… Keyboard input is much difficult to redirect.… So when a visitor tries to focus on the input they see on the page, they actually focus on the input… That would relax the restrictions, permitting scripts and forms.… -- ebook: prerender/ chrome headless dies and timeouts on this iframe --> Depending on your browser,

So, if we have a slotted element, and an event occurs somewhere inside it, then it bubbles up to the… All touch events and pointer events also have composed: true.… Custom events.When we dispatch custom events, we need to set both bubbles and composed properties to… For example, here we create div#inner in the shadow DOM of div#outer and trigger two events on it.… Pointer Events https://www.w3.org/TR/pointerevents. …And so on.

Event: submit.There are two main ways to submit a form: The first – to click <input type="submit… The second – press Enter on an input field. Both actions lead to submit event on the form.… Click <input type="submit">.… click When a form is sent using Enter on an input field, a click event triggers on the <… ;input type="submit">.

Capturing and bubbling allow us to implement one of the most powerful event handling patterns called… event delegation.… In the handler we get event.target to see where the event actually happened and handle it.… Just make a method and put it in the markup.… A document-wide handler tracks events, and if an event happens on an attributed element – performs the

Pointer events are a modern way to handle input from a variety of pointing devices, such as a mouse,… Events Level 3 is in the works and is mostly compatible with Pointer Events level 2.… ;event> events with pointer<event> in our code and expect things to continue working fine with… When the user moves and then removes a finger, we get pointermove and pointerup events with the same… ” process, and no more pointermove events are generated.

Understanding how event loop works is important for optimizations, and sometimes for the right architecture… Event Loop.The event loop concept is very simple.… When a user moves their mouse, the task is to dispatch mousemove event and execute handlers.… …and so on.… until the event bubbled up and was handled on all levels.

Another code may listen for the events and observe what’s happening with the menu.… MouseEvent, KeyboardEvent and others.Here’s a short list of classes for UI Events from the UI Event specification… Besides, the event class describes “what kind of event” it is, and if the event is custom, then we should… Such events are processed immediately: the new event handlers are called, and then the current event… The generic Event(name, options) constructor accepts an arbitrary event name and the options object with

the server and allows to receive events from it.… The browser will connect to url and keep the connection open, waiting for events.… The server should respond with status 200 and the header Content-Type: text/event-stream, then keep the… In such cases the "error" event will be emitted, and the browser won’t reconnect.… The server may specify another type of event with event: ... at the event start.

Taking something and dragging and dropping it is a clear and simple way to do many things, from copying… In the modern HTML standard there’s a section about Drag and Drop with special events such as dragstart… From the first sight it may seem that the mouse is always over the ball, and we can put mousemove on… And mouse events only happen on the top element, not on those below it.… And so on.

Second, more often we get a file from <input type="file"> or drag’n’drop or other browser… That’s how we can get a File object from <input type="file">:… Please note: The input… The most widely used events are for sure load and error.… We usually get File objects from user input, like <input> or Drag’n’Drop events (ondragend).

this chapter we’ll cover selection in the document, as well as selection in form fields, such as <input… Selection in form controls.Form elements, such as input and textarea provide special API for selection… Methods: input.select() – selects everything in the text control (can be textarea instead of input)… In this example we find "THIS" in the input text, replace it and keep the replacement selected… For input, textarea: additional methods and properties.

Forms and control elements, such as <input> have a lot of special properties and events.… This is typical with radio buttons and checkboxes.… Form elements.Let’s talk about form controls. input… and radio buttons.… In the next chapter we’ll cover focus and blur events that may occur on any element, but are mostly handled

Normally it goes upwards till <html>, and then to document object, and some events even reach window… But any handler may decide that the event has been fully processed and stop the bubbling.… Also we can write our data into the event object in one handler and read it in another one, so we can… In other words, normally the event goes first down (“capturing”) and then up (“bubbling”).… Bubbling and capturing lay the foundation for “event delegation” – an extremely powerful event handling

…And what if the loading failed?… Errors that may occur during script processing and execution are out of scope for these events.… Other resources.The load and error events also work for other resources, basically for any resource that… , save errors and provide an interface to access and analyze them.… Summary.Images <img>, external styles, scripts and other resources provide load and error events

corresponding to <input> has input-related properties and so on.… It is inherited by concrete HTML elements: HTMLInputElement – the class for <input> elements,… For example, let’s consider the DOM object for an <input> element.… , EventTarget – gives the support for events (to be covered), …and finally it inherits from Object, so… And if there was an <input> with a text entered by the visitor, then the text will be removed.

Otherwise, we re-download it again and put it in the cache for further possible reuse:… Once the new value (image) is downloaded and put into the cache, we register it in the finalizer registry… Creating “memories” and albums. Video montage from a series of photos. …and much more.… If not, it downloads it from the cloud and puts it in the cache for further use.… all the photos were downloaded from the cloud and put in it.

TextDecoder object allows one to read the value into an actual JavaScript string, given the buffer and… label – the encoding, utf-8 by default, but big5, windows-1251 and… …And then decode: input – BufferSource… This options tells TextDecoder to memorize “unfinished” characters and decode them when the next chunk

Run it and see what really happens.… And there are also focus/blur events that allow to catch the moment when the visitor focuses on a window… and switches elsewhere.… ads and evils pages.… Events focus and blur allow to track switching in and out of the window.

Export and import directives have several syntax variants.… …Or, technically we could put export above functions as well.… It makes code support and refactoring easier.… modules together and optimize them to speedup loading.… Summary.Here are all types of export that we covered in this and previous articles.

For instance, mousedown on an <input> field leads to focusing in it, and the focus event.… Try to click on the first <input> below – the focus event happens.… The focusing is still possible if we use another way to enter the input.… For instance, the Tab key to switch from the 1st input into the 2nd.… type="checkbox"> – checks/unchecks the input. submit – clicking an <input type="

properties index (position of the match), input (input string, equals str):… The function is called with arguments func(match, p1, p2, ..., pn, offset, input, groups): match – the… p1, p2, ..., pn – contents of capturing groups (if there are any), offset – position of the match, input… If there are no parentheses in the regexp, then there are only 3 arguments: func(str, offset, input).… repeatedly on different sources may fail If we apply the same global regexp to different inputs

See for…of and iterables for looping over arrays and iterable objects. Otherwise, please read on.… , while it’s truthy, execute it again and again.… The break directive is activated at the line (*) if the user enters an empty line or cancels the input… We need a way to stop the process if the user cancels the input… The ordinary break after input would only break the inner loop.

from the chapter Garbage collection, JavaScript engine keeps a value in memory while it is “reachable” and… It occupies memory and may not be garbage collected.… We put the data to a WeakMap, using the object as the key, and when the object is garbage collected,… Like Set, it supports add, has and delete, but not size, keys() and no iterations.… WeakSet is the absence of iterations, and the inability to get all current content.

But most environments have the internal scheduler and provide these methods.… In particular, they are supported in all browsers and Node.js. setTimeout.The syntax:… And here sayHi() runs the function, and the result of its execution is passed to setTimeout.… /setTimeout, an internal reference is created to it and saved in the scheduler.… loop: microtasks and macrotasks.

But technically no one limits us, and if there aren’t enough, we can add our own.… For instance, "type" is standard for <input> (HTMLInputElement), but not for <body… The attributes collection is iterable and has all the attributes of the element (standard and non-standard… ) as objects with name and value properties.… What if we use a non-standard attribute for our purposes and later the standard introduces it and makes

The caret ^ and dollar $ characters have special meaning in a regexp. They are called “anchors”.… The caret ^ matches at the beginning of the text, and the dollar $ – at the end.… For instance, to check if the user input is in the right format.… That is: two digits, then a colon, and then another two digits.… Anchors have “zero width” Anchors ^ and $ are tests. They have zero width.

Let’s say we have a string like +7(903)-123-45-67 and want to find all numbers in it.… A quantifier is appended to a character (or a character class, or a [...] set etc) and specifies how… The range: {3,5}, match 3-5 times To find numbers from 3 to 5 digits we can put the limits into curly… r looks for o followed by zero or one u, and then r. So, colou?… r finds both color and colour:

The first thing to do is to locate quoted strings, and then we can replace them.… ; and her "broom".… So the first match is "witch" and her "broom".… and ??… …But let’s test it on one more text input

Or, to put it more simply, when a promise is ready, its .then/catch/finally handlers are put into the… first and then caught.… We did catch and handle the error!”… with the “event loop” and “macrotasks”.… loop: microtasks and macrotasks.

It stores the date, time and provides methods for date/time management.… We can set out-of-range values, and it will auto-adjust itself.… So it’s faster and doesn’t put pressure on garbage collection.… And then you probably won’t need microbenchmarks at all.… Date and time in JavaScript are represented with the Date object.

bold), and previous remembered contexts are below.… And the optimization may be unneeded and totally not worth the efforts.… And they, potentially, can split even more.… And that’s sometimes required to optimize stuff.… But for many tasks a recursive solution is fast enough and easier to write and support.

used one of them (admin) to get into it and make changes.… We’ll mention that in the chapter Property flags and descriptors.… and copying them on the primitive level.… user[key] and, if it’s an object, then replicate its structure as well.… Summary.Objects are assigned and copied by reference.

The secret of reliability and simplicity of a coffee machine – all details are well-tuned and hidden… , and dangerous (it can electrocute).… Internal and external interface.In object-oriented programming, properties and methods are split into… Until now we were only using public properties and methods.… The code constantly undergoes development and improvement.

We can put both kinds of quotes in the square brackets: ['"](.*?)… ['"], but it would find strings with mixed quotes, like "...' and '...".… looks for the closing quote exactly the same as the opening one, we can wrap it into a capturing group and… The regular expression engine finds the first quote (['"]) and memorizes its content.… Similar to that, \2 would mean the contents of the second group, \3 – the 3rd group, and so on.

A Proxy object wraps another object and intercepts operations, like reading/writing properties and others… We don’t have to override value-adding array methods like push and unshift, and so on, to add checks… They are described in the article Private and protected properties and methods.… And very simple to implement.… object and the proxy.

Before we get into JavaScript’s ways of dealing with styles and classes – here’s an important rule.… JavaScript can modify both classes and style properties.… That’s more flexible and easier to support. className and classList.Changing a class is one of the most… infers style.marginLeft and style.marginTop from it.… The browser takes the computed value and makes all units fixed and absolute, for instance: height:20px

There may be any pattern instead of X and Y.… If it’s not so, then the potential match is skipped, and the search continues.… =\s), and there’s 30 somewhere after it (?… That is: match everything, in any context, and then filter by context in the loop.… , so we know where exactly in the text it is, and can check the context.

New proposals to the language appear regularly, they are analyzed and, if considered worthy, are appended… to the list at https://tc39.github.io/ecma262/ and then progress to the specification.… It can parse (“read and understand”) modern code and rewrite it using older syntax constructs, so that… A transpiler would analyze our code and rewrite height ?? 100 into (height !… It “fills in” the gap and adds missing implementations.

Regular expressions are patterns that provide a powerful way to search and replace in text.… Regular Expressions.A regular expression (also “regexp”, or just “reg”) consists of a pattern and optional… The “long” syntax: And the “short”… And, finally, if there are no matches, null is returned (doesn’t matter if there’s flag g or not).… A regular expression consists of a pattern and optional flags: g, i, m, u, s, y.

That’s why Map and Set also exist.… So we should use map methods: set, get and so on. Map can also use objects as keys.… And the standard iteration for map returns same key/value pairs as map.entries().… For example, we have visitors coming, and we’d like to remember everyone.… But this may help to replace Map with Set in certain cases with ease, and vice versa.

For instance, [a-z] is a character in range from a to z, and [0-5] is a digit from 0 to 5.… similar characters, Join_Control (Join_C) – two special codes 200c and 200d, used in ligatures, e.g.… Unicode properties are covered in more details in the article Unicode: flag "u" and class \… They are denoted by a caret character ^ at the start and match any character except the given ones.… And if we need a backslash, then we use \\, and so on.

Specification.The ECMA-262 specification contains the most in-depth, detailed and formalized information… MDN (Mozilla) JavaScript Reference is the main manual with examples and other information.… To see their support among browser-based and other engines, see: https://caniuse.com – per-feature tables… caniuse.com/#feat=cryptography. https://kangax.github.io/compat-table – a table with language features and

They can be passed around, used as objects, and now we’ll see how to forward calls between them and decorate… …And for objects that are both iterable and array-like, such as a real array, we can use any of them,… Because we are calling hash(arguments), and arguments object is both iterable and array-like, but not… Append glue and this[1]. Append glue and this[2]. …Do so until this.length items are glued.… E.g. a decorator may count how many times a function was invoked and how much time it took, and expose

The “Same Origin” (same site) policy limits access of windows and frames to each other.… If we set any event handlers on it, they will be ignored.… can put a space-delimited list of those that we want to lift.… It has some JavaScript and a form. Please note that nothing works.… both agree and call corresponding JavaScript functions.

Getters and setters.Accessor properties are represented by “getter” and “setter” methods.… It is readable and writable.… the access is done via getter and setter.… a setter and tweak its behavior.… We can try to find all such places and fix them, but that takes time and can be hard to do if that code