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There are two kinds of custom elements: Autonomous custom elements – “all-new” elements, extending the… Customized built-in elements – extending built-in elements, like a customized button, based on HTMLButtonElement… Custom element name must contain a hyphen - Custom element name must have a hyphen -, e.g… That leads to important consequences for custom elements.… Compatiblity: https://caniuse.com/#feat=custom-elementsv1.

CSS animations make it possible to do simple animations without JavaScript at all.… CSS transitions.The idea of CSS transitions is simple.… The syntax for a Bezier curve in CSS: cubic-bezier(x2, y2, x3, y3).… During a CSS animation, this process repeats every frame.… CSS transforms never affect neighbour elements.

Custom events can be used to create “graphical components”.… Later we’ll see what it means for custom events.… The bubbling mechanics is the same for built-in (click) and custom (hello) events.… In the second argument (object) we can add an additional property detail for any custom information that… For custom events we should use CustomEvent constructor.

JavaScript allows to use throw with any argument, so technically our custom error classes don’t need… That may become a bit tedious – to assign this.name = <class name> in every custom error class.… And then inherit all our custom errors from it. Let’s call it MyError.… Here’s the code with MyError and other custom error classes, simplified:… Now custom

CSS hooks with custom properties.How do we style internal elements of a component from the main document… But just as we expose methods to interact with our component, we can expose CSS variables (custom CSS… Custom CSS properties exist on all levels, both in light and shadow.… CSS custom properties pierce through shadow DOM.… They are used as “hooks” to style the component: The component uses a custom CSS property to style key

CSS styles, applied to the component.… Usually, special CSS classes and conventions are used to provide “component feel” – CSS scoping and DOM… Custom elements – to define custom HTML elements.… CSS Scoping – to declare styles that only apply inside the Shadow DOM of the component.… Event retargeting and other minor stuff to make custom components better fit the development.

prop: works as value.prop, if value exists, otherwise (when value is undefined/null) it returns undefined… prop – returns obj.prop if obj exists, otherwise undefined. obj?.… [prop] – returns obj[prop] if obj exists, otherwise undefined. obj.method?.

of operations and Reflect calls that do the same: Operation Reflect call Internal method obj[prop… ] Reflect.get(obj, prop) [[Get]] obj[prop] = value Reflect.set(obj, prop, value) [[Set]] delete obj… [prop] Reflect.deleteProperty(obj, prop) [[Delete]] new F(value) Reflect.construct(F, value) [[Construct… , receiver) can be replaced by target[prop].… A call to target[prop], when prop is a getter, runs its code in the context this=target.

Such as <input type="range">: The browser uses DOM/CSS internally to draw them.… We can use it style subelements with CSS, like this:… Shadow tree can be used in Custom Elements to hide component internals and apply component-local styles… The elem must be either a custom element, or one of: “article”, “aside”, “blockquote”, “body”, “div”,

Just like built-in browser <select> expects <option> items, our <custom-tabs> may expect… And a <custom-menu> may expect menu items.… The code that makes use of <custom-menu> can look like this:… That’s possible, but if we’re moving elements to shadow DOM, then CSS styles from the document do not… There are many <li slot="item"> in the <custom-menu>, but only one <slot name

But what about non-standard, custom ones? First, let’s see whether they are useful or not?… Sometimes non-standard attributes are used to pass custom data from HTML to JavaScript, or to “mark”… But there may be a possible problem with custom… Using data-* attributes is a valid, safe way to pass custom… Then CSS updates the view accordingly: in the example above the last line (*) changes the color to blue

querySelector.The call to elem.querySelector(css) returns the first element for the given CSS selector… The elem.matches(css) does not look for anything, it merely checks if elem matches the given CSS-selector… The method elem.closest(css) looks for the nearest ancestor that matches the CSS-selector.… Besides that: There is elem.matches(css) to check if elem matches the given CSS selector.… There is elem.closest(css) to look for the nearest ancestor that matches the given CSS-selector.

We should always prefer CSS classes to style.… Mind the units.Don’t forget to add CSS units to values.… : A computed style value is the value after all CSS rules and CSS inheritance is applied, as the result… of the CSS cascade.… Visited links may be colored using :visited CSS pseudoclass.

this: Here’s how it looks with some CSS… We can add nested lists and style them using CSS to “slide down”.… don’t abuse Technically, by preventing default actions and adding JavaScript we can customize… But if we make a button behave as a link using JavaScript and even look like a link using CSS, then &

“what is” CSS width and height.… A change in box-sizing for CSS purposes may break such JavaScript.… So the real width available for the content is less than CSS width.… Firefox) – CSS width (ignore the scrollbar).… The element with text has CSS width:300px.

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 also set a custom logic in the static method Symbol.hasInstance.… That’s how we can customize the behavior of instanceof.… Symbol.toStringTag.The behavior of Object toString can be customized… steroids” that not only works for primitive data types, but also for built-in objects and even can be customized

between window-relative coordinates and CSS position:fixed.… But in CSS positioning, right property means the distance from the right edge, and bottom property means… To show something near an element, we can use getBoundingClientRect to get its coordinates, and then CSS… will appear under it The code can be modified to show the message at the left, right, below, apply CSS… coordinate systems have their pros and cons; there are times we need one or the other one, just like CSS

CSSOM for styling There’s also a separate specification, CSS Object Model (CSSOM) for CSS… In practice though, the CSSOM is rarely required, because we rarely need to modify CSS rules from JavaScript… (usually we just add/remove CSS classes, not modify their CSS rules), but that’s also possible.

JavaScript animations can handle things that CSS can’t.… setInterval.An animation can be implemented as a sequence of frames – usually small changes to HTML/CSS… in callback then they will be grouped together with other requestAnimationFrame callbacks and with CSS… Unlike CSS, we are not limited to Bezier curves here.… The same is true about draw: we can animate anything, not just CSS properties.

CSS events: transitionend – when a CSS-animation finishes. There are many other events.… We could also use objects of a custom class, like this:

And we can use it in CSS rules too.… The pattern has two parts: We add a custom attribute to an element that describes its behavior.

Although, we may need to add touch-action: none in some places in CSS.… To avoid problems with them too: Prevent them by setting #ball { touch-action: none } in CSS.… Let’s recall how one can implement a custom slider, described in the Drag'n'Drop with mouse events.… and handle on its own – remember to cancel the default action on events and set touch-action: none in CSS

That wrapper returns a promise and forwards the call to the original f, tracking the result in the custom… Then our custom callback is in exactly the right format, and promisify works great for such a case.

There are many ways to initiate a scroll, so it’s more reliable to use CSS, overflow property.

If that’s not what we want, then soon we’ll see how to customize the process.… Custom “toJSON”.Like toString for string conversion, an object may provide method toJSON for to-JSON… Now let’s add a custom toJSON for our object room (2):

Custom events.When we dispatch custom events, we need to set both bubbles and composed properties to

Even more, we can customize that behavior.

For instance, CSS\d matches a string CSS with a digit after it:

JavaScript doesn’t allow you to customize how operators work on objects.… In this chapter we’ll cover how an object converts to primitive and how to customize it.… Let’s implement these methods to customize the conversion.

syntax: This means that property prop

To handle such complex cases we may need to use a combination of cloning methods, write custom code or… copy” (nested objects are copied by reference) or a “deep cloning” function structuredClone or use a custom

Bezier curves are used in computer graphics to draw shapes, for CSS animation and in many other places… but very needed insight into what Bezier curves are, while the next one shows how we can use them for CSS… In CSS animation to describe the path and speed of animation.

For example: To handle custom events… The server may set a custom event name in event:.

At the right part of the tools there are the following subtabs: Styles – we can see CSS applied to the… Computed – to see CSS applied to the element by property: for each property we can see a rule that gives… it (including CSS inheritance and such).

For instance, "for (let prop in obj)" is also widely used.

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/CSS

It’s forbidden to generate “custom” clipboard events with dispatchEvent in all browsers except Firefox

In the chapter Dispatching custom events we saw an example: custom event menu-open is dispatched in setTimeout

The handler should analyze errors (custom error classes help) and rethrow unknown ones (maybe they are

Non-enumerable.Now let’s add a custom

bundlers – they give more control over how modules are resolved, allowing bare modules and much more, like CSS… “Special” module types like HTML/CSS modules are also supported.

Custom properties.We can also add properties of our own.

This feature allows us to integrate custom objects with promise chains without having to inherit from

This algorithm can’t be changed or customized.

That’s usually doable with CSS.

The Sources panel has 3 parts: The File Navigator pane lists HTML, JavaScript, CSS

One of them is to use custom events, we’ll cover them later.

So right now old browsers still may show it as a message, but aside of that – there’s no way to customize

HTTP-headers.XMLHttpRequest allows both to send custom headers and read headers from the response.