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).
Further on, we’ll use the modern shadow DOM standard, covered by DOM spec and other related specifications… 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.
They form text nodes and become a part of the DOM.… Even if it doesn’t exist in the document, it will exist in the DOM, because the browser will create it… 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.
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”.
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.
: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
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.
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.… Now let’s create the same div with JavaScript (assuming that the styles are in the HTML/CSS already).… 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.
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… For instance, the href DOM property is always a full URL, even if the attribute contains a relative URL… The value of the DOM property may be different, for instance the href property is always a full URL,
Each DOM node belongs to the corresponding built-in class.… 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
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.
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
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.
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.
</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.
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 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 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 ending point also has <p> as the parent node, but 2 as the offset (it specifies the range up… It’s only important that the end is after the start in the document.… 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:… DOM spec: Range
Selection API
HTML spec: APIs for the text control selections
Summary.We covered two
For mouseover:
event.target – is the element where the mouse came over.
event.relatedTarget – is the… For mouseout the reverse:
event.target – is the element that the mouse left.
event.relatedTarget – is… 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… As you can see, the only generated events are the ones related to moving the pointer in and out of the
How do we find the width and height of the browser window?… 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.
An element receives the focus when the user either clicks on it or uses the Tab key on the keyboard.… we can run the code to initialize the required functionality.… Losing the focus generally means: “the data has been entered”, so we can run the code to check it or… If an element is removed from DOM, then it also causes the focus loss.… The value of the attribute is the order number of the element when Tab (or something like that) is used
The root is the built-in Event class.… If the event was created with the bubbles flag, then it bubbles.… In the example below the click event is initiated in JavaScript.… For instance, in the code below the menu-open event is triggered during the onclick.… The propagation and handling of the nested event is finished before the processing gets back to the outer
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.… user visited a link by creating it on the page and checking the styles.… Summary.To manage classes, there are two DOM properties:
className – the string value, good to manage… The style.cssText property corresponds to the whole "style" attribute, the full string of styles
Then on the outer <div>.
Then on the outer <form>.… the event, it doesn’t change through the bubbling process.
this – is the “current” element, the one… The standard DOM Events describes 3 phases of event propagation:
Capturing phase – the event goes down… The target triggers at the end of the first and at the beginning of the second phase.… the event.
event.currentTarget (=this) – the current element that handles the event (the one that has
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… So, without scrollbar the content width would be 300px, but if the scrollbar is 16px wide (the width… 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.
event object allows to get the character, while the code property of the event object allows to get… Read the alphanumeric section of the spec for more codes, or just press a key in the teststand above.… 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
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
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 onblocked handler (in the new tab) to alert the visitor, tell him that the newer version can’t be… The request.result for add is the key of the new object.
The error is in request.error (if any).… with the given value at the keyPath.… 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
The quote is detected, and then the engine tries to find a match for the rest of the pattern… The engine keep backtracking: it decreases the count of repetition for '.' until the rest of the pattern… The first step is the same: it finds the pattern start '"' at the 3rd position:… Then the number of repetitions is increased again and again…
…Till the match for the rest of the pattern… work the similar way – the regexp engine increases the number of repetitions only if the rest of the
The callback gets one argument – the time passed from the beginning of the page load… In the graph above the regular bounce has the red color, and the easeOut bounce is blue.… Regular bounce – the object bounces at the bottom, then at the end sharply jumps to the top.… easeInOut.We also can show the effect both in the beginning and the end of the animation.… As we can see, the graph of the first half of the animation is the scaled down easeIn, and the second
The word “modal” means that the visitor can’t interact with the rest of the page, press other buttons… title
The text to show the visitor.
default
An optional second parameter, the initial value for the input… 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.
the kind, not the name, so it should stick with the function keyword.… Then, as shown at the picture above, the result of yield gets into the question variable in the calling… The second .next(4) passes 4 back to the generator as the result of the first yield, and resumes the… The third next(9) passes 9 into the generator as the result of the second yield and resumes the execution… in the examples above, the outer code may pass a value into the generator, as the result of yield.
For instance, in the code below the URL to fetch is wrong (no such site) and .catch handles the error… execution jumps from the first .catch (*) to the next one (**) down the chain.… The script dies with a message in the console.… event is the part of the HTML standard.… probably report the incident to the server.
When the property changes, the browser paints the animation.… The x axis is the time: 0 – the start, 1 – the end of transition-duration.… The y axis specifies the completion of the process: 0 – the starting value of the property, 1 – the final… The y is out of the “standard” range 0..1.… The alternative value end would mean that the change should be applied not in the beginning, but at the
While the condition is truthy, the code from the loop body is executed.… The loop in the example above makes three iterations.… the process.… It stops the loop immediately, passing control to the first line after the loop. Namely, alert.… process if the user cancels the input.
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.… below highlights and outputs the tag of the element that is now in the middle of the window:… But note the important detail: when the page is scrolled, the message flows away from the button.… of the window while the page scrolls away.
When we access something inside the embedded window, the browser checks if the iframe has the same origin… How to detect the moment when the document is there?… – the reference to the “parent” (outer) window.
window.top – the reference to the topmost parent window… The event object has special properties:
data
The data from postMessage.
origin
The origin of the sender… of the sender window (like http://my.site.com)
source – the reference to the sender window.
data – the
The arr.findIndex method has the same syntax but returns the index where the element was found instead… As the function is applied, the result of the previous function call is passed to the next one as the… the next array element:
sum
current
result
the first call
0
1
1
the second call
1
2
3
the… The calculation table is the same as above, minus the first row.… For the full list, see the manual.
The next then (***) gets the result of the previous one, processes it (doubles) and passes it to the… on the same promise get the same result – the result of that promise.… So in the code above all alert show the same: 1.… on to the handler of the second .then.… We’ll use the fetch method to load the information about the user from the remote server.
The setTimeout above schedules the next call right at the end of the current one (*).… This way the next call may be scheduled differently, depending on the results of the current one.… In this case the engine waits for func to complete, then checks the scheduler and if the time is up,… Each call remembers the real time from the previous one in the times array.… The browser tab is in the background mode.
The laptop is on battery saving mode.
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