All DOM nodes generate such signals (but events are not limited to DOM).… HTML-attribute.A handler can be set in HTML with an attribute named on<event>.… But generally we use only one of these ways.… The event object is also available in HTML handlers
If we assign a handler in HTML, we can… HTML attributes are used sparingly, because JavaScript in the middle of an HTML tag looks a little bit
But what if we’d like to insert an HTML string “as html”, with all tags and stuff working, in the same… " – insert html into elem, at the beginning,
"beforeend" – insert html into elem, at the… The second parameter is an HTML string, that is inserted “as HTML”.… The html string can be dynamically generated, so it’s kind of flexible.… Given some HTML in html, elem.insertAdjacentHTML(where, html) inserts it depending on the value of where
The backbone of an HTML document is tags.… According to the Document Object Model (DOM), every HTML tag is an object.… For instance, the top tag is always <html>.… lt;html> and <body>, and add the required <head>, and the DOM will be:
While generating… …etc, everything in HTML has its place in DOM, even comments.
When the browser loads the page, it “reads” (another word: “parses”) the HTML and generates DOM objects… HTML attributes.In HTML, tags may have attributes.… These methods operate exactly with what’s written in HTML.… HTML-elements for JavaScript.… We want to read the value “as written” in HTML.
Usually the HTML-mode is used for webpages.… ="more html".… HTML of the element.The outerHTML property contains the full HTML of the element.… With innerHTML we’ll have it inserted “as HTML”, with all HTML tags.… Can safely insert user-generated text and protect from unwanted HTML insertions.
hidden
When set to true
This chapter is about sending HTML forms: with or without files, with additional fields and so on.… As you might have guessed, it’s the object to represent HTML form data.… The constructor is:
If HTML form element… Summary.FormData objects are used to capture HTML form and submit it using fetch or another network method… We can either create new FormData(form) from an HTML form, or create an object without a form at all,
For instance, server-side scripts that download HTML pages and process them can also use the DOM.… Specifications
The BOM is a part of the general HTML specification.… The HTML spec at https://html.spec.whatwg.org is not only about the “HTML language” (tags, attributes… That’s “HTML in broad terms”.… HTML specification
Describes the HTML language (e.g. tags) and also the BOM (browser object model) –
But generally we should try to keep the code simple and self-descriptive.… Also, there are tools like JSDoc 3 that can generate HTML-documentation from the comments.… Comments are also used for auto-documenting tools like JSDoc3: they read them and generate HTML-docs
There’s also an autofocus HTML attribute that puts the focus onto an element by default when a page loads… Focusing on an element generally means: “prepare to accept the data here”, so that’s the moment when… Losing the focus generally means: “the data has been entered”, so we can run the code to check it or… In practice though, one should think well, before implementing something like this, because we generally… This can be changed using HTML-attribute tabindex.
In other words, a module can provide a generic functionality that needs a setup.… wait until the HTML document is fully ready (even if they are tiny and load faster than HTML), and then… As a side effect, module scripts always “see” the fully loaded HTML-page, including HTML elements below… Async scripts run immediately when ready, independently of other scripts or the HTML document.… “Special” module types like HTML/CSS modules are also supported.
Generator functions.To create a generator, we need a special syntax construct: function*, so-called “… generator function”.… Generators may generate values forever
In the examples above we generated finite sequences… syntax to generate values.… Generators are created by generator functions function* f(…) {…}.
Here it is:
The HTML is like this:… In our case if we take a look inside the HTML, we can see nested tags inside <td>, like <strong… The HTML structure is flexible, we can add/remove buttons at any time.… Not buttons, but the general approach is important here.… We can add new ones to HTML at any moment.
The lifecycle of an HTML page has three important events:
DOMContentLoaded – the browser fully loaded… HTML, and the DOM tree is built, but external resources like pictures <img> and stylesheets may… not yet have loaded.
load – not only HTML is loaded, but also all the external resources: images, styles… DOMContentLoaded and scripts.When the browser processes an HTML-document and comes across a <script… There’s also a keepalive flag for doing such “after-page-left” requests in fetch method for generic
By clicking on a link you download a dynamically-generated Blob with hello world contents as a file:… Here’s the similar code that causes user to download the dynamically created Blob, without any HTML:… link.href looks like:
For each URL generated… A generated URL (and hence the link with it) is only valid within the current document, while it’s open… In the previous example with the clickable HTML-link, we don’t call URL.revokeObjectURL(link.href), because
They can be written right in a web page’s HTML and run automatically as the page loads.… For instance, in-browser JavaScript is able to:
Add new HTML to the page, change the existing content… Different tabs/windows generally do not know about each other.… There are at least three great things about JavaScript:
Full integration with HTML/CSS.… JavaScript has a unique position as the most widely-adopted browser language, fully integrated with HTML
That’s fine for simple scripts, inlined into HTML, but generally isn’t a good thing.… Also, when one reads JS code and doesn’t have HTML in view, it’s not obvious where the variable comes… the collection with elements that the pointer is over now (in nesting order: from the outermost <html
Normally it goes upwards till <html>, and then to document object, and some events even reach window… capturing phase was invisible for us, because handlers added using on<event>-property or using HTML… If you click on <p>, then the sequence is:
HTML → BODY → FORM → DIV -> P (capturing phase,… the first listener):
P → DIV → FORM → BODY → HTML (bubbling phase, the second listener).… the event bubbles up from event.target to the root, calling handlers assigned using on<event>, HTML
In this HTML, a click on a link doesn’t lead to navigation; the browser doesn’t do anything:… some CSS:
Menu items are implemented as HTML-links… But we should generally keep the semantic meaning of HTML elements.… Besides being “just a good thing”, that makes your HTML better in terms of accessibility.
Generators are labelled with function* (note the star) and use yield to generate a value, then we can… generates a sequence of values, we can use an asynchronous generator.… It’s generated by GitHub itself.… Summary.Regular iterators and generators work fine with the data that doesn’t take time to generate.… :
Generators
Async generators
Declaration
function*
async function*
next() return value is
Its HTML has two nested elements: the <div id="child"> is inside the <div id="… but one thing we know for sure: if the pointer “officially” entered an element (mouseover event generated… triggers, when the pointer moves from an element to its descendant, e.g. from #parent to #child in this HTML… As you can see, the only generated events are the ones related to moving the pointer in and out of the
Here in the picture we use the word “line”, as in our example there’s only one subcall in line, but generally… For web-developers there are much better-known examples: HTML and XML documents.… In the HTML document, an HTML-tag may contain a list of:
Text pieces.
HTML-comments.… Other HTML-tags (that in turn may contain text pieces/comments or other tags etc).… Trees like HTML elements tree or the department tree from this chapter are also naturally recursive:
The JavaScript engine tracks such rejections and generates a global error in that case.… The event is the part of the HTML
Touch devices also generate similar events when one taps on them.… The problem is: a left-click with Ctrl is interpreted as a right-click on MacOS, and it generates the… Surely the user has access to HTML-source of the page, and can take the content from there, but not everyone
The full HTML page with these frameworks and pow spec:… The HTML element <div id="mocha"> will be used by Mocha to output results.… Instead of writing it blocks manually, we can generate them in for:… But in general writing tests makes development faster and more stable.
Sec-WebSocket-Key – a random browser-generated key, used to ensure that the server supports WebSocket… Rate limiting.Imagine, our app is generating… HTML: we need a <form> to send messages and a <div> for incoming messages:
Selection.Range is a generic object for managing selection ranges.… As an input value is a pure text, not HTML, there’s no need for such objects, everything’s much simpler… Some browsers generate it, but we shouldn’t rely on it.… DOM spec: Range
Selection API
HTML spec: APIs for the text control selections
Summary.We covered two
For example, we need that to store a list of something: users, goods, HTML elements etc.… The for..in loop is optimized for generic objects, not arrays, and thus is 10-100 times slower.… Generally, we shouldn’t use for..in for arrays.
chapter Blob),
"document" – get as XML document (can use XPath and other XML methods) or HTML… It generates events, similar to xhr, but xhr.upload triggers them solely on uploading:
loadstart – upload
However, most of the generally used properties are animatable.
transition-duration.In transition-duration… Here’s a list of digits, without any animations, just as a source:
Resultstyle.cssindex.htmlIn the HTML
A built-in <template> element serves as a storage for HTML markup templates.… In theory, we could create any invisible element somewhere in HTML for HTML markup storage purposes.… First, its content can be any valid HTML, even if it normally requires a proper enclosing tag.… Summary.To summarize:
<template> content can be any syntactically correct HTML… The <template> tag is quite unique, because:
The browser checks HTML syntax inside it (as opposed
For instance, we need to find programming languages: HTML, PHP, Java or JavaScript.… The corresponding regexp: html|php|java(script)?.… To apply alternation to a chosen part of the pattern, we can enclose it in parentheses:
I love HTML|… CSS matches I love HTML or CSS.… I love (HTML|CSS) matches I love HTML or I love CSS.
We can create custom HTML elements, described by our class, with its own methods and properties, events… Once a custom element is defined, we can use it on par with built-in HTML elements.… That’s great, as HTML dictionary is rich, but not infinite.… That’s strange for an HTML element.… HTML Living Standard: https://html.spec.whatwg.org/#custom-elements.
Regexp for an “opening HTML-tag… Improved: /<[a-z][a-z0-9]*>/i
According to the standard, HTML tag name may have a digit at any… Regexp “opening or closing HTML-tag without attributes”: /<\/?… For instance, for HTML tags we could use a simpler regexp: <\w+>.… But as HTML has stricter restrictions for a tag name, <[a-z][a-z0-9]*> is more reliable.
The “script” tag.JavaScript programs can be inserted almost anywhere into an HTML document using the… used nowadays but can still be found in old code:
The type attribute: <script type=…>
The old HTML… Also, the modern HTML standard totally changed the meaning of this attribute.… Script files are attached to HTML with the src attribute:… Please note:
As a rule, only the simplest scripts are put into HTML
documentElement and body.The topmost tree nodes are available directly as document properties:
<html… That’s the DOM node of the <html> tag.… For instance, <head> and <body> are children of <html> element.… This detail may be useful when we want to travel up from an arbitrary element elem to <html>, but… There are also additional navigation properties for HTML forms.
Such snippet in an HTML markup looks like this:… We find code snippets in HTML and highlight them.
Now let’s go on.… For now it only matters that we fetch an HTML article from a webserver and display it on demand:… The new article HTML may contain code snippets… We can add/remove code snippets in HTML without thinking about it.
</textarea> holds its value as nested HTML, we should never use textarea.innerHTML to access it… It stores only the HTML that was initially on the page, not the current value.… text – the text inside the option,
value – the option value,
defaultSelected – if true, then selected HTML-attribute… The difference between defaultSelected and selected is that defaultSelected sets the HTML-attribute (
In modern websites, scripts are often “heavier” than HTML: their download size is larger, and processing… When the browser loads HTML and comes across a <script>...… example, the browser notices the script (and can start downloading it) only after it downloaded the full HTML… For long HTML documents, that may be a noticeable delay.… Instead, the browser will continue to process the HTML, build DOM.
information, we can use the root document element document.documentElement, that corresponds to the <html… DOCTYPE HTML> in HTML. Odd things are possible.
In modern HTML we should always write DOCTYPE.
We can not only assign handlers, but also generate events from JavaScript.… We can generate not only completely new events, that we invent for our own purposes, but also built-in… Browser-generated events always have the right type.… Summary.To generate an event from code, we first need to create an event object.… We shouldn’t generate browser events as it’s a hacky way to run handlers.
Or we have a class User and a class EventEmitter that implements event generation, and we’d like to add… An important feature of many browser objects (for instance) is that they can generate events.… Or, a menu can generate the event "select" when a menu item is selected, and other objects… Summary.Mixin – is a generic object-oriented programming term: a class that contains methods for other… So generally one should think well about the naming methods of a mixin, to minimize the probability of
Some features are well-supported and integrated into the modern HTML/DOM standard, while others are yet… Custom elements – to define custom HTML elements.
And JavaScript generally has no concept of “aborting” a promise.… Generally, we have two parties in the process:
The one that performs a cancelable operation, it sets… AbortController is a simple object that generates an abort event on its signal property when the abort
Further inheritance.The ValidationError class is very generic. Many things may go wrong.… The human-readable message is generated by the constructor.… have SyntaxError and ValidationError, but in the future readUser function may grow and probably generate… If the readUser function generates several kinds of errors, then we should ask ourselves: do we really… We’ll make a new class ReadError to represent a generic “data reading” error.
tree.A DOM element can have two types of DOM subtrees:
Light tree – a regular DOM subtree, made of HTML… Shadow tree – a hidden DOM subtree, not reflected in HTML, hidden from prying eyes.
The brief history.Let’s make a small overview, so that you understand the general picture and the place… For the existing scripts to work, they generated (and still generate) mouse events.… For instance, tapping a touchscreen generates mousedown.… Browser-generated.… native drag’n’drop support for images, that kicks in and takes over the drag’n’drop process, thus generating
If json is malformed, JSON.parse generates an error, so the script “dies”.… “Throw” operator.The throw operator generates an error.… Let’s see what kind of error JSON.parse generates… a SyntaxError with the given message, the same way as JavaScript would generate it itself.… We can also generate our own errors using the throw operator.
Where’s the code that generates… But that is generally a bad idea.… So, generally, modifying a native prototype is considered a bad idea.
Rabbit class should be based on Animal, have access to animal methods, so that rabbits can do what “generic… That’s why dates have access to generic object methods.… That may be useful for advanced programming patterns when we use functions to generate classes depending… a class extends another class and has no constructor, then the following “empty” constructor is generated… Methods are not “free”.As we’ve known before, generally functions are “free”, not bound to objects in
Iterable objects are a generalization of arrays.… object, a so-called “iterator” is created by the call to range[Symbol.iterator](), and its next() generates… Or we can make an iterable object that generates an infinite sequence of pseudorandom numbers.
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