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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.

We can create custom HTML elements, described by our class, with its own methods and properties, events… 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.

But they also may have other properties of their own, e.g.… The parent constructor sets the message property.… (property).… And then inherit all our custom errors from it. Let’s call it MyError.… Then name property can be used for such checks.

Property-attribute synchronization.When a standard attribute changes, the corresponding property is auto-updated… DOM properties are typed.DOM properties are not always strings.… Properties – is what’s in DOM objects.… A small comparison: Properties Attributes Type Any value, standard properties have types described… The value of the DOM property may be different, for instance the href property is always a full URL,

The exception is when a local property is labelled !… properties) to style it.… 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

As we know, objects can store properties.… Until now, a property was a simple “key-value” pair to us.… But an object property is actually a more flexible and powerful thing.… Property flags.Object properties, besides a value, have three special attributes (so-called “flags”):… Object.isSealed(obj) Returns true if adding/removing properties is forbidden, and all existing properties

We can also set a custom logic in the static method Symbol.hasInstance.… That’s how we can customize the behavior of instanceof.… That can lead to interesting consequences when a prototype property is changed after the object is created… Symbol.toStringTag.The behavior of Object toString can be customized… using a special object property Symbol.toStringTag.

Naturally, such a string should include all important properties.… are added, old properties are renamed and removed.… in properties?… If we pass an array of properties to it, only these properties will be encoded.… But the list of properties is quite long.

When we perform actions with the object, e.g. take a property user.name, the JavaScript engine looks… The value of user is constant, it must always reference the same object, but properties of that object… We’ll mention that in the chapter Property flags and descriptors.… Nested cloning.Until now we assumed that all properties of user are primitive.… But properties can be references to other objects.

Their internal implementation uses the object’s constructor property for that.… Even more, we can customize that behavior.… That was thoroughly explained in the article Static properties and methods.

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:… Here’s the markup for <custom-menu>:… There are many <li slot="item"> in the <custom-menu>, but only one <slot name

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”,… element with a shadow root is called a “shadow tree host”, and is available as the shadow root host property… If mode="open", then it’s accessible as elem.shadowRoot property.

Connection status: readyState.The EventSource object has readyState property, that has one of three values… We can query this property to know the state of EventSource.… For example: To handle custom events… The current state is in the readyState property.… The server may set a custom event name in event:.

This is governed by the composed event object property.… Custom events.When we dispatch custom events, we need to set both bubbles and composed properties to

The “name” property.Function objects contain some useable properties.… Custom properties.We can also add properties of our own.… Function properties can replace closures sometimes.… Here we covered their properties: name – the function name.… Also, functions may carry additional properties.

DOM property.We can assign a handler using a DOM property on<event>.… As there’s only one onclick property, we can’t assign more than one event handler.… There are more properties.… DOM property: elem.onclick = function.… DOM properties are ok to use, but we can’t assign more than one handler of the particular event.

It’s forbidden to generate “custom” clipboard events with dispatchEvent in all browsers except Firefox… The event.clipboardData property gives access to the clipboard.

Methods and properties are: new Map() – creates the map. map.set(key, value) – stores the value by the… This algorithm can’t be changed or customized.… Methods and properties: new Map([iterable]) – creates the map, with optional iterable (e.g. array) of… Additional convenient methods, the size property. Set – is a collection of unique values.… Methods and properties: new Set([iterable]) – creates the set, with optional iterable (e.g. array) of

Once the server has responded, we can receive the result in the following xhr properties… We can also specify a timeout using the corresponding property:… Response Type.We can use xhr.responseType property… note: In the old scripts you may also find xhr.responseText and even xhr.responseXML properties… HTTP-headers.XMLHttpRequest allows both to send custom headers and read headers from the response.

Although, mouse events don’t have necessary properties to handle such multi-touches.… touch events were introduced, such as touchstart, touchend, touchmove, that have touch-specific properties… We can use this property to react differently on various pointer types.… These properties aren’t supported by most devices, so they are rarely used.… Device-specific properties, such as pressure, width/height, and others.

There are other non-standard properties available in most environments.… Throwing our own errors.What if json is syntactically correct, but doesn’t have a required name property… And in the browser we can assign a function to the special window.onerror property, that will run in… That JS script sets a custom window.onerror function.… Error objects have following properties: message – the human-readable error message. name – the string

One of them is to use custom events, we’ll cover them later.… In fact, the capturing phase was invisible for us, because handlers added using on<event>-property… There’s a property event.eventPhase that tells us the number of the phase on which the event was caught… Each handler can access event object properties: event.target – the deepest element that originated

The reason for this is that the script may want to get coordinates and other style-dependent properties… This event is available via the onload property.… So right now old browsers still may show it as a message, but aside of that – there’s no way to customize… The document.readyState property tells us about the current loading state.

Now let’s add a custom constructor to Rabbit.… A derived constructor has a special internal property [[ConstructorKind]]:"derived".… [[HomeObject]].To provide the solution, JavaScript adds one more special internal property for functions… When a function is specified as a class or object method, its [[HomeObject]] property becomes that object… Internals: Methods remember their class/object in the internal [[HomeObject]] property.

Chrome), passive is true by default for touchstart and touchmove events. event.defaultPrevented.The property… don’t abuse Technically, by preventing default actions and adding JavaScript we can customize

There are two kinds of object properties. The first kind is data properties.… All properties that we’ve been using until now were data properties.… The second type of property is something new. It’s an accessor property.… Accessor descriptors.Descriptors for accessor properties are different from those for data properties… as for data properties, configurable – same as for data properties.

That actually does the same as assigning it as a property… such code won’t work: Static properties… Static properties are also possible, they look like regular class properties, but prepended by static… and methods.Static properties and methods are inherited.… Static properties are used when we’d like to store class-level data, also not bound to an instance.

Forms and control elements, such as <input> have a lot of special properties and events.… They also have elements property that lists form controls inside them.… select and option.A <select> element has 3 important properties: select.options – the collection… The elements property also works for <fieldset>. element.form Elements reference their form in… the form property.

DOM node classes.Different DOM nodes may have different properties.… corresponding to <input> has input-related properties and so on.… The tagName property exists only for Element nodes.… DOM nodes also have other properties depending on their class.… Most standard HTML attributes have a corresponding DOM property.

Until now we were only using public properties and methods.… Now we’ll make a coffee machine in JavaScript with all these types of properties.… Let’s change waterAmount property to protected to have more control over it.… Protected properties are usually prefixed with an underscore _.… Read-only “power”.For power property, let’s make it read-only.

Custom elements – to define custom HTML elements.… Event retargeting and other minor stuff to make custom components better fit the development.… In the next chapter we’ll go into details of “Custom Elements” – the fundamental and well-supported feature

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.

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.

A property is a “key: value” pair, where key is a string (also called a “property name”), and value can… In the user object, there are two properties: The first property has the name "name" and the… That’s called computed properties.… Property value shorthand.In real code, we often use existing variables as values for property names.… The use-case of making a property from a variable is so common, that there’s a special property value

Such properties are called “inherited”.… The __proto__ property is a bit outdated.… So writing to such a property is actually the same as calling a function.… And for..in only lists enumerable properties.… Properties from the prototype are not taken into account. Summary.

The only thing that worked reliably was a "prototype" property of the constructor function,… Please note that F.prototype here means a regular property named "prototype" on F.… It sounds something similar to the term “prototype”, but here we really mean a regular property with… If, after the creation, F.prototype property changes (F.prototype = <another object>), then new… Default F.prototype, constructor property.Every function has the "prototype" property even

"> Write properties directly into style: <div style="...">.… JavaScript can modify both classes and style properties.… There’s another property for that: elem.classList.… getComputedStyle requires the full property name We should always ask for the exact property… To change the styles: The style property is an object with camelCased styles.

It doesn’t have own properties.… property, and so on.… passed as the first argument to new Proxy, property – property name, receiver – if the target property… The set trap triggers when a property is written. set(target, property, value, receiver): target – is… – property value, receiver – similar to get trap, matters only for setter properties.

And also Unicode property search becomes available, we’ll get to it next.… Unicode properties \p{…}.Every character in Unicode has a lot of properties.… We can search for characters with a property, written as \p{…}.… There are shorter aliases for almost every property.… Unicode properties can be used in the search: \p{…}.

We describe a property and how its changes should be animated.… When the property changes, the browser paints the animation.… them together in the order: property duration timing-function delay, as well as animating multiple properties… one by one. transition-property.In transition-property, we write a list of properties to animate, for… Luckily, the transform property is very powerful.

/Top.These properties are rarely needed, but still they are the “most outer” geometry properties, so… Geometry properties are zero/null for elements that are not displayed Geometry properties… To measure them, there are properties clientTop and clientLeft.… We can use these properties to expand the element wide to its full width/height.… Why should we use geometry properties instead?

The prototype property of a constructor function has worked since very ancient times.… The __proto__ property is special: it must be either an object or null.… As we know, __proto__ is not a property of an object, but an accessor property of Object.prototype:… Now it is processed as a regular data property, so the example above works right.… or Object.create(proto[, descriptors]), allows to specify property descriptors.

That’s a part of the general “hiding symbolic properties” principle.… That said, all symbols have the description property.… Symbols have two main use cases: “Hidden” object properties.… a symbol and use it as a property key.… properties.

Properties firstChild and lastChild give fast access to the first and last children.… The for..in loop iterates over all enumerable properties.… The next sibling is in nextSibling property, and the previous one – in previousSibling.… These properties are usually the same: they both get the parent.… There are also additional navigation properties for HTML forms.

The function might only require certain elements or properties.… The left side contains an object-like “pattern” for corresponding properties.… In the example above the property width goes to w, property height goes to h, and title is assigned to… In the code below options has another object in the property size and an array in the property items.… Object properties that have no mapping are copied to the rest object.

is a safe way to access nested object properties, even if an intermediate property doesn’t exist.… The “non-existing property” problem.If you’ve just started to read the tutorial and learn JavaScript,… As you can see, property names are still duplicated in the code.… Further properties are accessed in a regular way.… allows to safely access nested properties. Still, we should apply ?.

closely, we may notice two operations in obj.method() statement: First, the dot '.' retrieves the property… The result of a property access user.hi is not a function, but a value of Reference Type.… Reading a property, such as with dot . in obj.method() returns not exactly the property value, but a… special “reference type” value that stores both the property value and the object it was taken from.… For all other operations, the reference type automatically becomes the property value (a function in

Main DOMRect properties: x/y – X/Y-coordinates of the rectangle origin relative to window, width/height… Derived properties can be easily calculated from them: left = x top = y right = x + width bottom = y… Why derived properties are needed? Why does top/left exist if there’s x/y?… So the additional derived properties are for convenience.… But in CSS positioning, right property means the distance from the right edge, and bottom property means

All properties of the global object can be accessed directly:… become the property of the global object:… If a value is so important that you’d like to make it available globally, write it directly as a property… In-browser, unless we’re using modules, global functions and variables declared with var become a property… To make our code future-proof and easier to understand, we should access properties of the global object

It has a single method abort(), And a single property signal that allows to set event listeners on it… abort() is called: controller.signal emits the "abort" event. controller.signal.aborted property… Using with fetch.To be able to cancel fetch, pass the signal property of an AbortController as a fetch… AbortController is a simple object that generates an abort event on its signal property when the abort… method is called (and also sets signal.aborted to true). fetch integrates with it: we pass the signal property