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Add/remove items.We already know methods that add and remove items from the beginning or the end: arr.push… , one after another: item is the element. index is its index. array is the array itself.… – is the current array item. index – is its position. array – is the array.… Summary.A cheat sheet of array methods: To add/remove elements: push(...items) – adds items to the… If any of items is an array, then its elements are taken.

, but fruits.pop() also modifies the array by removing it.… If new Array is called with a single argument which is a number, then it creates an array without items… We can use an array as a deque with the following operations: push(...items) adds items to the end.… Instead you can use for..of loop to compare arrays item-by-item.… We will continue with arrays and study more methods to add, remove, extract elements and sort arrays

Arrays are used for storing ordered collections. But that’s not enough for real life.… Map.Map is a collection of keyed data items, just like an Object.… t exist in map. map.has(key) – returns true if the key exists, false otherwise. map.delete(key) – removes… the element (the key/value pair) by the key. map.clear() – removes everything from the map. map.size… Not necessarily an array.

A department may have an array of staff.… methods to get the sum of the array.… …But there’s a problem with arrays.… items in any place.… In an array that’s easy: arr[n] is a direct reference.

Here’s an example of using these methods to add items to a list and the text before/after it:… All insertion methods automatically remove the node from the old place.… Why append to a special kind of node, if we can return an array of nodes instead?… Old-school insert/remove methods.… parentElem.removeChild(node) Removes node from parentElem (assuming node is its child).

setItem(key, value) – store key/value pair. getItem(key) – get the value by key. removeItem(key) – remove… ) – delete everything. key(index) – get the key on a given position. length – the number of stored items… Looping over keys.As we’ve seen, the methods provide “get/set/remove by key” functionality.… One way is to loop over them as over an array:… clear() – delete everything. key(index) – get the key number index. length – the number of stored items

…And the method .off(name, handler) that removes the handler listener.… Or, a menu can generate the event "select" when a menu item is selected, and other objects… Technically, there’s an _eventHandlers property that stores an array of handlers for each event name,… and it just adds it to the list. .off(eventName, handler) – removes the function from the handlers list

If we pass an array of properties to it, only these properties will be encoded.… Fortunately, we can use a function instead of an array as the replacer.… items.… can include other objects and arrays.… JSON supports plain objects, arrays, strings, numbers, booleans, and null.

A key must be one of these types – number, date, string, binary, or array.… /removed/altered during a version update.… Add the item to their inventory.… The price is not an array, so multiEntry flag is not applicable.… Then getAll will fail to get all records as an array. What to do?

We’ll make a numeric array that returns 0 for nonexistent values.… Usually when one tries to get a non-existing array item, they get undefined, but we’ll wrap a regular… For instance, Map stores items in the internal slot [[MapData]].… Array has no internal slots A notable exception: built-in Array doesn’t use internal slots… So there’s no such problem when proxying an array.

Typed arrays behave like regular arrays: have indexes and are iterable.… If an Array, or any array-like object is given, it creates a typed array of the same length and copies… These methods allow us to copy typed arrays, mix them, create new arrays from existing ones, and so on… For typed arrays, the constructor dictates what the format is.… Unlike typed arrays, DataView doesn’t create a buffer on its own.

Arrays allow us to gather data items into an ordered list.… is skipped, the third one is assigned to title, and the rest of the array items are also skipped (as… The rest ‘…’.Usually, if the array is longer than the list at the left, the “extra” items are omitted… In the code below options has another object in the property size and an array in the property items.… The full array syntax: The first item

That has two effects: It allows to get a part of the match as a separate item in the result array.… , the corresponding result array item is present and equals undefined.… We can turn it into a real Array using Array.from.… item, we can write: (?… in the results array.

And a <custom-menu> may expect menu items.… ="item"> in the template.… So all such <li slot="item"> are appended to <slot name="item"> one after… Updating slots.What if the outer code wants to add/remove menu items dynamically?… After 1 second: slotchange: item triggers, when a new <li slot="item"> is added.

Of course, Arrays are iterable.… Array-likes are objects that have indexes and length, so they look like arrays.… a “real” Array from it.… , then makes a new array and copies all items to it.… use array methods on it.

Usually, properties of an object or elements of an array… For instance, if we put an object into an array, then while the array is alive, the object will be alive… we use an object as the key in it, and there are no other references to that object – it will be removed… We need to clean visitsCountMap when we remove users, otherwise it will grow in memory indefinitely.… After john object becomes unreachable, by all means except as a key of WeakMap, it gets removed from

And also, how to pass arrays to such functions as parameters.… The dots literally mean “gather the remaining parameters into an array”.… But the downside is that although arguments is both array-like and iterable, it’s not an array.… Spread syntax.We’ve just seen how to get an array from the list of parameters.… The list of characters is passed to array initializer [...str].

For instance, when we create an array [1, 2, 3], the default new Array() constructor is used internally… For instance, if we’re making an array-like object, we may want to copy some Array methods to it.… It doesn’t check if the object is indeed an array. Many built-in methods are like that.… __proto__ to Array.prototype, so all Array methods are automatically available in obj.… The object itself stores only the data (array items, object properties, the date) Primitives also store

The apply accepts only array-like args.… …And for objects that are both iterable and array-like, such as a real array, we can use any of them,… a real array.… …Do so until this.length items are glued. Return result.… It is quite common to take array methods and apply them to arguments.

For instance: arr.forEach(func) – func is executed by forEach for every array item. setTimeout(func)

node, subtree – in all descendants of node, attributes – attributes of node, attributeFilter – an array… an element for a "childList" mutation, addedNodes/removedNodes – nodes that were added/removed… Naturally, the third-party script provides no mechanisms to remove it.… Using MutationObserver, we can detect when the unwanted element appears in our DOM and remove it.… We can add/remove code snippets in HTML without thinking about it.

It’s easy to find a file by its name or add/remove a file.… We can add, remove and read files from it at any time.… To remove… Makes it easier to add/remove/move around properties, because all lines become alike.… Summary.Objects are associative arrays with several special features.

DOM collections.As we can see, childNodes looks like an array.… But actually it’s not an array, but rather a collection – a special array-like iterable object.… Array methods won’t work, because it’s not an array:… The second is tolerable, because we can use Array.from to create a “real” array from the collection,… If we keep a reference to elem.childNodes, and add/remove nodes into DOM, then they appear in the collection

constructor syntax is: blobParts is an array… URL.revokeObjectURL(url) removes the reference from the internal mapping, thus allowing the Blob to be… After the revocation, as the mapping is removed, the URL doesn’t work any more.… can easily convert between Blob and low-level binary data types: We can make a Blob from a typed array

They are supported for: Map Set Array Plain objects also support similar methods, but the syntax is… Object.values(obj) – returns an array of values.… Object.entries(obj) – returns an array of [key, value] pairs.… Use array methods on that array, e.g. map, to transform these key/value pairs.… Use Object.fromEntries(array) on the resulting array to turn it back into an object.

Built-in classes like Array, Map and others are extendable also.… of results using exactly arr.constructor, not basic Array.… If we’d like built-in methods like map or filter to return regular arrays, we can return Array in Symbol.species… For instance, Array extends Object.… But Array.

Promise.all takes an iterable (usually, an array… The new promise resolves when all listed promises are resolved, and the array of their results becomes… For instance, the Promise.all below settles after 3 seconds, and then its result is an array [1, 2, 3… A common trick is to map an array of job data into an array of promises, and then wrap that into Promise.all… But if any of those objects is not a promise, it’s passed to the resulting array “as is”.

Sometimes that’s what we need, but often we want to add/remove a single class.… The elem.classList is a special object with methods to add/remove/toggle a single class.… Methods of classList: elem.classList.add/remove("class") – adds/removes the class. elem.classList.toggle… Then later we may want to remove the style.display as if it were not set.… So, We can remove a property like this:

Remove the breakpoint by right-clicking and selecting Remove. …And so on.… If you click on a stack item (e.g.

It monitors all objects and removes those that have become unreachable.… If we overwrite admin too, then it can be removed. Interlinked objects.Now a more complex example.… Now let’s remove two references:… All objects except marked ones are removed.… The unmarked ones are then removed. That’s the concept of how garbage collection works.

object with two properties: done – true when the reading is complete, otherwise false. value – a typed array… We gather response chunks in the array chunks.… At the end, we have chunks – an array of Uint8Array byte chunks.… there’s some code to do that: We create chunksAll = new Uint8Array(receivedLength) – a same-typed array… It’s a byte array though, not a string. To create a string, we need to interpret these bytes.

If an element is removed from DOM, then it also causes the focus loss.… Click the first item and press Tab:

An additional optional object with properties: once: if true, then the listener is automatically removed… To remove the handler, use removeEventListener:… Removal requires the same function To remove a handler we should… doesn’t work: The handler won’t be removed… Methods: elem.addEventListener(event, handler[, phase]) to add, removeEventListener to remove.

It has 3 modes: If the regexp doesn’t have flag g, then it returns the first match as an array with… If there are no matches, we don’t get an empty array, but null.… There are 3 differences from match: It returns an iterable object with matches instead of an array.… We can make a regular array from it using Array.from.… Every match is returned as an array with capturing groups (the same format as str.match without flag

It has 3 working modes: If the regular expression has flag g, it returns an array of all matches:… If there’s no such flag it returns only the first match in the form of an array, with the full match… The array… If there are no matches, we don’t receive an empty array, but instead receive null.… If we’d like the result to always be an array

…And with built-in classes like Array… That’s because Array prototypically inherits from Object.… boolean, it will be [object Boolean] For null: [object Null] For undefined: [object Undefined] For arrays… : [object Array] …etc (customizable).

See for…of and iterables for looping over arrays and iterable objects. Otherwise, please read on.… We can also remove… We can actually remove everything, creating an infinite loop:

We can add/remove <td> dynamically at any time and the highlighting will still work.… The HTML structure is flexible, we can add/remove buttons at any time.… Less code: when adding or removing elements, no need to add/remove handlers.… DOM modifications: we can mass add/remove elements with innerHTML and the like.

JavaScript can access an existing selection, select/deselect DOM nodes as a whole or partially, remove… range content from the document extractContents() – remove range content from the document and return… range from the selection. removeAllRanges() – remove all ranges. empty() – alias to removeAllRanges.… them is selected. selectAllChildren(node) – select all children of the node. deleteFromDocument() – remove… In its simplest one-argument form it replaces the user selected range and removes the selection.

Object.seal(obj) Forbids adding/removing of properties.… Object.freeze(obj) Forbids adding/removing/changing of properties.… Object.isSealed(obj) Returns true if adding/removing properties is forbidden, and all existing properties… Object.isFrozen(obj) Returns true if adding/removing/changing properties is forbidden, and all current

not form field name), as it were a name of the file in user’s filesystem, formData.delete(name) – remove… The difference is that .set removes all fields with the given name, and then appends a new field.… name, value) formData.set(name, blob, fileName) Let’s note two peculiarities here: The set method removes

The structuredClone method can clone most data types, such as objects, arrays… All operations via copied references (like adding/removing properties) are performed on the same single

To do so, we can find and remove anything that’s not a number.… An alternative, shorter way is to find non-digits \D and remove them from the string:… We can’t add or remove spaces from a regular expression and expect it to work the same.

If we remove the protective cover from the coffee machine, then using it will be much more complex (where… It was made by the “Best CoffeeMachine” company, and works fine, but a protective cover was removed.… That’s surely not John’s fault, but rather the person who removed the protective cover and let John do… great to know that private methods can be safely renamed, their parameters can be changed, and even removed

In the code above, ...generateSequence() turns the iterable generator object into an array… of items (read more about the spread syntax in the chapter Rest parameters and spread syntax) Using

Also, note that the new top menu item named “Develop” has appeared.

similar to Blob: fileParts – is an array… Please note: The input may select multiple files, so input.files is an array-like

spaces (just like any character) in the document, then they become text nodes in the DOM, and if we remove… For instance, $0.style.background = 'red' makes the selected list item red, like this:

Now let’s remove the semicolon after the alert:… They remove comments, so they don’t appear in the working scripts.

"Very plain" objects.As we know, objects can be used as associative arrays to store key/value… Now, if we intend to use an object as an associative array and be free of such problems, we can do it… …But that’s usually fine for associative arrays