They form text nodes and become a part of the DOM.… Then the browser creates <tbody> in the DOM automatically.… We may think – why is a comment added to the DOM?… Another way to explore the DOM is to use the browser developer tools.… From the next chapter on we’ll access and modify DOM using JavaScript.
DOM modification is the key to creating “live” pages.… Here we’ll see how to create new elements “on the fly” and modify the existing page content.… But the alternative way would be to clone the existing div and modify the text inside it (if needed).… The method comes from times when there was no DOM, no standards… Really old times.… It writes directly into the page text, while the DOM is not yet built.
The DOM allows us to do anything with elements and their contents, but first we need to reach the corresponding… All operations on the DOM start with the document object. That’s the main “entry point” to DOM.… That’s the DOM node of the <html> tag.… DOM world null means “doesn’t exist”
In the DOM, the null value means “doesn’t exist” or… will put it in the DOM).
slots of the shadow DOM.… Now the element has both light and shadow DOM.… " with the same name in the light DOM.… So, the flattened DOM is derived from shadow DOM by inserting slots.… The result is called a “flattened DOM”.
DOM (Document Object Model).The Document Object Model, or DOM for short, represents all page content… Properties and methods are described in the specification: DOM Living Standard.… DOM is not only for browsers
The DOM specification explains the structure of a document and… The CSSOM is used together with the DOM when we modify style rules for the document.… Now, we’ll get down to learning the DOM, because the document plays the central role in the UI.
When the browser loads the page, it “reads” (another word: “parses”) the HTML and generates DOM objects… For instance, if the tag is <body id="page">, then the DOM object has body.id="page… When the browser parses the HTML to create DOM objects for tags, it recognizes standard attributes and… In the example below id is modified as an attribute, and we can see the property changed too.… The value of the DOM property may be different, for instance the href property is always a full URL,
Element – is the base class for DOM elements.… Instead, it replaces it in the DOM.… In the outer document (the DOM) we can see the new content instead of the <div>.… The outerHTML assignment does not modify the DOM element (the object referenced by, in this case, the… Can be modified.
outerHTML
The full HTML of the element.
Using MutationObserver, we can detect when the unwanted element appears in our DOM and remove it.… Well, we can do it on DOMContentLoaded event, or put the script at the bottom of the page.… The moment our DOM is ready, we can search for elements pre[class*="language"] and call Prism.highlightElem… That is, if a node is removed from the DOM, and becomes unreachable, then it can be garbage collected… The mere fact that a DOM node is observed doesn’t prevent the garbage collection.
Each event may be useful:
DOMContentLoaded event – DOM is ready, so the handler can lookup DOM nodes… The DOM tree is ready – here’s the event. There are few peculiarities though.… > tag, it needs to execute before continuing building the DOM.… We’d like our function to execute when the DOM is loaded, be it now or later.… Summary.Page load events:
The DOMContentLoaded event triggers on document when the DOM is ready.
The connectedCallback triggers when the element is added to the document.… Rendering order.When HTML parser builds the DOM, elements are processed one after another, parents before… That’s exactly because there are no children on that stage, the DOM is unfinished.… So the outer element finishes the initialization before the inner one.… There may be different tags that share the same DOM-class, that’s why specifying
The ending point also has <p> as the parent node, but 2 as the offset (it specifies the range up… Otherwise, to copy the full DOM, e.g. if we need to keep formatting, we can get the underlying ranges… Here’s the demo of copying the selected content both as text and as DOM nodes:… selection.To modify the content of the selection, we can use input.setRangeText() method.… DOM spec: Range
Selection API
HTML spec: APIs for the text control selections
Summary.We covered two
The style property operates only on the value of the "style" attribute, without any CSS cascade… A resolved style value is the one finally applied to the element.… Summary.To manage classes, there are two DOM properties:
className – the string value, good to manage… Reading and writing to it has the same meaning as modifying individual properties in the "style&… The style.cssText property corresponds to the whole "style" attribute, the full string of styles
We’ll see the details later in the chapter Shadow DOM slots, composition.… from the light DOM.… In particular, Shadow DOM elements may have ids that conflict with those in the light DOM.… Style rules from the outer DOM don’t get applied.… Shadow DOM, if exists, is rendered by the browser instead of so-called “light DOM” (regular children)
:host.The :host selector allows to select the shadow host (the element containing the shadow tree).… It matches elements based on two conditions:
That’s a slotted element, that comes from the light DOM… The element matches the selector.… There’s no selector that can directly affect shadow DOM styles from the document.… For example, in shadow DOM we can use --user-card-field-color CSS variable to style fields, and the
But scripts in the main document have no idea about the shadow DOM internals, especially if the component… Events that happen in shadow DOM have the host element as the target, when caught outside of the component… That’s an element from the light DOM, so no retargeting.… That’s exactly the parent chain from the target element in the flattened DOM, after the composition.… Then it’s out of the component shadow DOM, but won’t bubble up to higher-level DOM.
The element looks like this:
You can open the document in the sandbox… Mind the scrollbar
The picture above demonstrates the most complex case when the element… The scrollbar is then not on the right, but on the left, and then clientLeft also includes the scrollbar… provide the size of the area inside the element borders.… scrollLeft/scrollTop can be modified
Most of the geometry properties here are read-only,
event object allows to get the character, while the code property of the event object allows to get… You can find the list in the specification.… On the other hand, event.code has the benefit of staying always the same, bound to the physical key location… As we know, the false value returned from the event handler, assigned using a DOM property or an attribute… There we can check the new input.value and modify it/highlight the <input> when it’s invalid.
Some features are well-supported and integrated into the modern HTML/DOM standard, while others are yet… A good architect is the one who can make the complex simple.… CSS styles, applied to the component.… Shadow DOM – to create an internal DOM for the component, hidden from the others.… CSS Scoping – to declare styles that only apply inside the Shadow DOM of the component.
the onblocked handler (in the new tab) to alert the visitor, tell him that the newer version can’t be… An object store can only be created/modified while updating the DB version, in upgradeneeded… The request.result for add is the key of the new object.
The error is in request.error (if any).… default, the cursor walks up from the record with the lowest key.… In the example above the cursor was made for the object store.
That had the benefit of never breaking existing code.… in the language forever.… It added new features to the language and modified some of the existing ones.… When it is located at the top of a script, the whole script works the “modern” way.… In the next chapters, as we learn language features, we’ll see the differences between the strict and
Here’s a list of the most useful DOM events, just to take a look at:
Mouse events:
click – when the… Document events:
DOMContentLoaded – when the HTML is loaded and processed, DOM is fully built.… attribute content and writes it to the DOM property.… For instance, the DOMContentLoaded event, that triggers when the document is loaded and the DOM has been… DOM properties are ok to use, but we can’t assign more than one handler of the particular event.
browser detects the invalid DOM structure and “fixes” it, adds <table> around.… The content becomes live (styles apply, scripts run etc) when we insert it into the document.… They form the shadow DOM:
Summary.To… The <template> tag is quite unique, because:
The browser checks HTML syntax inside it (as opposed… The content becomes interactive: scripts run, <video autoplay> plays etc, when inserted into the
</script> tag, it can’t continue building the DOM. It must execute the script right now.… Instead, the browser will continue to process the HTML, build DOM.… The script loads “in the background”, and then runs when the DOM is fully built.… Scripts with defer always execute when the DOM is ready (but before DOMContentLoaded event).… The DOM and other scripts don’t wait for them, and they don’t wait for anything.
For mouseover:
event.target – is the element where the mouse came over.
event.relatedTarget – is the… That means that if the visitor is moving the mouse very fast then some DOM-elements may be skipped:… In particular, it’s possible that the pointer jumps right inside the middle of the page from out of the… The pointer is still over the parent, it just moved deeper into the child element.… As you can see, the only generated events are the ones related to moving the pointer in and out of the
is checked for a strict equality to the value from the first case (that is, value1) then to the second… If the equality is found, switch starts to execute the code starting from the corresponding case, until… the nearest break (or until the end of switch).… The values must be of the same type to match.… But for 3, the result of the prompt is a string "3", which is not strictly equal === to the
In attempting to click the link, the visitor in fact clicks the button.… The demo.Here’s how the evil page looks.… A click on the button actually clicks on the iframe, but that’s not visible to the user, because the… we need to attack – is to position the <iframe> on the evil page in such a way that the button… So when a visitor tries to focus on the input they see on the page, they actually focus on the input
In other words, var variables are defined from the beginning of the function, no matter where the definition… is (assuming that the definition is not in the nested function).… The var inside it is processed in the beginning of the function, so at the moment of (*) the variable… The declaration is processed at the start of function execution (“hoisted”), but the assignment always… parentheses around the function is a trick to show JavaScript that the function is created in the context
Once the element is removed from the DOM, the logger will notice it and stop sending messages.… Now let’s take a closer look at the source code (tab index.js):
Get the DOM-element of the “Start sending… Get the DOM-element of the “Close” button.… Get the DOM-element of the logs display window using the new WeakRef() constructor.… This way, the windowElementRef variable holds a weak reference to the DOM-element.
The browser tries to help us by mixing namespaces of JS and DOM.… It looks for the given id in the whole document.… So it’s faster and also shorter to write.
matches.Previous methods were searching the DOM.… The ancestors together form the chain of parents from the element to the top.… If it matches the selector, then the search stops, and the ancestor is returned.
The toggler button opens the tab with files.… The Code Editor pane shows the source code.… on within the code of the example page.… the debugger (after we’ve set the breakpoints) is to reload the page.… opens the console at the bottom.
function is created with the arguments arg1...argN and the given functionBody.… All previous declarations required us, programmers, to write the function code in the script.… It references the Lexical Environment from where it’s created (we covered that in the chapter Variable… The code of that function is not known at the time of writing the script (that’s why we don’t use regular… not the outer one.
expression on the right side with their use and returns its result.… Upon the execution, it evaluates the expression a + b and returns the result.… eyes get used to the structure.… They took arguments from the left of =>, evaluated and returned the right-side expression with them… : the function evaluates it and returns the result.
The click may occur not on the <td>, but inside it.… :
The method elem.closest(selector) returns the nearest ancestor that matches the selector.… That’s important, because otherwise this inside it would reference the DOM element (elem), not the Menu… It’s one of the most helpful patterns for DOM events.… DOM modifications: we can mass add/remove elements with innerHTML and the like.
The general algorithm of the engine:
While there are tasks:
execute them, starting with the oldest… Changes to the DOM are painted only after the task is complete.… While the engine is busy with syntax highlighting, it can’t do other DOM-related stuff, process user… As mentioned earlier, changes to DOM are painted only after the currently running task is completed,… Here’s the demo, the changes to i won’t show up until the function finishes, so we’ll see only the last
The "prototype" property is widely used by the core of JavaScript itself.… The obj is empty!… of the other.… It works because the internal algorithm of the built-in join method only cares about the correct indexes… All built-in objects follow the same pattern:
The methods are stored in the prototype (Array.prototype
Modifiers: shift, alt, ctrl and meta.All mouse events include the information about pressed modifier… For instance, if we have a window of the size 500x500, and the mouse is in the left-upper corner, then… And if the mouse is in the center, then clientX and clientY are 250, no matter what place in the document… Move the mouse over the input field to see clientX/clientY (the example is in the iframe, so coordinates… Surely the user has access to HTML-source of the page, and can take the content from there, but not everyone
object is stored somewhere in memory (at the right of the picture), while the user variable (at the… at what’s at that address and performs the operation on the actual object.… We can use either variable to access the object and modify its contents:… It copies the properties of all source objects into the target dest, and then returns it as the result… clone, not the user!
by the user.… Can’t prevent anything in oninput
The input event occurs after the value is modified.… That’s because technically the data isn’t in the clipboard yet.… So the example above uses document.getSelection() to get the selected text.… The action can be prevented. The event.clipboardData property gives access to the clipboard.
If we ever need to change the message or the way it is shown, it’s enough to modify the code in one place… For instance, in the code below the function uses the local userName.… When the execution reaches it, the function stops, and the value is returned to the calling code (assigned… There must be an agreement within the team on the meaning of the prefixes.… only get).
createForm – would be bad if it modifies the document, adding a form to it (should only create
The point is that length treats 4 bytes as two 2-byte characters.… We’ll see that a bit later, in the article Sets and ranges [...].… Here’s the main character categories and their subcategories:
Letter L:
lowercase Ll
modifier Lm,
titlecase… Symbol S:
currency Sc,
modifier Sk,
math Sm,
other So.… Unicode properties can be used in the search: \p{…}.
The method Object.getOwnPropertyDescriptor allows to query the full information about a property.… The syntax is:
obj
The object to get… information from.
propertyName
The name of the property.… The returned value is a so-called “property descriptor” object: it contains the value and all the flags… the addition of new properties to the object.
When the page is scrolled to the very beginning, so that the top/left corner of the window is exactly… the distance from the bottom edge.… “coords-show-mark”, the message will appear under it
The code can be modified to show the message at… But note the important detail: when the page is scrolled, the message flows away from the button.… The modified createMessageUnder function:
the data.… null if the key is newly added).
newValue – the new value (null if the key is removed).
url – the url… Please note that the event also contains: event.url – the url of the document where the data was updated… localStorage, so event.storageArea references the one that was modified.… Contains all the data about the operation (key/oldValue/newValue), the document url and the storage object
The word “modal” means that the visitor can’t interact with the rest of the page, press other buttons… The call to prompt returns the text from the input field or null if the input was canceled.… the rest of the page until the window has been dismissed.… Usually, it’s in the center.
The exact look of the window also depends on the browser.… We can’t modify it.
That is the price for simplicity.
.
params
The configuration string for the new window.… (top = true)
Scroll the window to make elem show up at the top (the default) or at the bottom for elem.scrollIntoView… The intention is to “lock” the user within the window.… The popup may access the opener window using the window.opener property.… The main window and the popup can freely read and modify each other if they have the same origin.
And in the line (**) the property has a setter in the prototype, so it is called.… The value of “this”.An interesting question may arise in the example above: what’s the value of this… In a method call, this is always the object before the dot.… And when the inheriting objects run the inherited methods, they will modify only their own states, not… the state of the big object.
How do we get the full width and height of the document, including the scrolled out part?… In other words, they return the width/height of the visible part of the document, available for the content… Important:
To scroll the page with JavaScript, its DOM must be fully built.… on the top of the window.… The drawback of the method is that the scrollbar disappears.
Usually that header is set automatically and contains the url of the page that made the request.… Unlike the referrer option that allows to set the exact Referer value, referrerPolicy tells the browser… That is, it respects the Expires and Cache-Control headers, sends If-Modified-Since and so on.… But the keepalive option tells the browser to perform the request in the background, even after it leaves… the page.
The server accepts the POST request and replies “User saved”.… name), as it were a name of the file in user’s filesystem,
formData.delete(name) – remove the field… with the given name,
formData.get(name) – get the value of the field with the given name,
formData.has… The difference is that .set removes all fields with the given name, and then appends a new field.… The server reads form data and the file, as if it were a regular form submission.
The JavaScript language steadily evolves.… to the list at https://tc39.github.io/ecma262/ and then progress to the specification.… The more good stuff – the better!… Usually, a developer runs the transpiler on their own computer, and then deploys the transpiled code… to the server.
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