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That declaration is called an object literal.… literal, when creating an object.… Ordered like an object.Are objects ordered?… What we’ve studied in this chapter is called a “plain object”, or just Object.… Objects in JavaScript are very powerful.

The global object provides variables and functions that are available anywhere.… Recently, globalThis was added to the language, as a standardized name for a global object, that should… The global object holds variables that should be available everywhere.… The global object has a universal name globalThis.… We should store values in the global object only if they’re truly global for our project.

There are no networking methods that require exactly a URL object, strings are good enough.… the string conversion, that turns a URL object into a string with full URL.… So there’s a URL property for that: url.searchParams, an object of type URLSearchParams.… The good news is that URL objects handle all that automatically.… As of now, URL objects are often more convenient, but strings can still be used as well.

programming When we write our code using objects to represent entities, that’s called object-oriented… “this” in methods.It’s common that an object method needs to access the information stored in the object… Calling without an object: this == undefined We can even call the function without an object… always have this referencing that object.… A function can be copied between objects.

In JavaScript, functions are objects.… A good way to imagine functions is as callable “action objects”.… We can not only call them, but also treat them as objects: add/remove properties, pass by reference etc… The “name” property.Function objects contain some useable properties.… Summary.Functions are objects. Here we covered their properties: name – the function name.

One of the fundamental differences of objects versus primitives is that objects are stored and copied… Objects are not like that.… A variable assigned to an object stores not the object itself, but its “address in memory” – in other… Comparison by reference.Two objects are equal only if they are the same object.… object.

expect a “summed” object as the result.… But we left a gap for objects.… All built-in objects except for one case (Date object, we’ll learn it later) implement "default&… string "[object Object]".… as a string, like in an alert or so, then by default we see [object Object].

It’s the oldest way to create objects with a given prototype.… We can call such objects “very plain” or “pure dictionary” objects, because they are even simpler than… the regular plain object {...}.… A downside is that such objects lack any built-in object methods, e.g. toString:… With null prototype, objects are truly empty.

Object]"?… …But the short notation obj = {} is the same as obj = new Object(), where Object is a built-in object… As we remember, they are not objects.… Remember, we only can inherit from one object at a time.… The object itself stores only the data (array items, object properties, the date) Primitives also store

We could try to loop over properties in it, but what if the object is complex and has nested objects… JSON.stringify.The JSON (JavaScript Object Notation) is a general format to represent values and objects… JSON.parse to convert JSON back into an object.… Please note that a JSON-encoded object has several important differences from the object literal: Strings… That’s why the first line is ":[object Object]" in the example above.

That’s because Array prototypically inherits from Object.… are converted to string as [object Object]:… For a number, it will be [object Number] For a boolean, it will be [object Boolean] For null: [object… Null] For undefined: [object Undefined] For arrays: [object Array] …etc (customizable).… , objects with Symbol.toStringTag string instanceof objects true/false As we can see, {}.toString

For instance, if we put an object into an array, then while the array is alive, the object will be alive… as the key in a regular Map, then while the Map exists, that object exists as well.… We put the data to a WeakMap, using the object as the key, and when the object is garbage collected,… An object exists in the set while it is reachable from somewhere else.… A membership in WeakSet may mean something about the object.

For instance, if there’s an object in a global variable, and that object has a property referencing another… object, that object is considered reachable.… The source object is the same as above.… All visited objects are remembered, so as not to visit the same object twice in the future.… Incremental collection – if there are many objects, and we try to walk and mark the whole object set

Map can also use objects as keys.… The same does not count for Object.… String as a key in Object is fine, but we can’t use another Object as a key in Object.… , it converts all Object keys, such as john and ben above, to same string "[object Object]"… The differences from a regular Object: Any keys, objects can be keys.

WeakRef – is an object, that contains a weak reference to another object, called target or referent.… In other words, a WeakRef object does not keep the referent object alive.… object you want a weak reference to).… The deref() method returns the referent-object that the WeakRef points to, if the object is still in… deleting the object from memory.

The regular {...} syntax allows us to create one object.… With new we all know that the new object is being created.… the object is returned instead of this.… In other words, return with an object returns that object, in all other cases this is returned.… Objects, we’ll be back!

Let’s look at the key distinctions between primitives and objects.… An object Is capable of storing multiple values as properties.… There are other kinds of objects in JavaScript: functions, for example, are objects.… So here we’ve made an object john with the method sayHi.… Objects are “heavier” than primitives.

Remember, new objects can be created with a constructor function, like new F().… If F.prototype is an object, then the new operator uses it to set [[Prototype]] for the new object.… If, after the creation, F.prototype property changes (F.prototype = <another object>), then new… objects created by new F will have another object as [[Prototype]], but already existing objects keep… The value of F.prototype should be either an object or null: other values won’t work.

A Proxy object wraps another object and intercepts operations, like reading/writing properties and others… same value as [[GetPrototypeOf]] applied to the proxy object’s target object.… So we bind the context of object methods to the original object, target, in the line (*).… = target.The proxy and the original object are different objects. That’s natural, right?… object and the proxy.

object.… DOM (Document Object Model).The Document Object Model, or DOM for short, represents all page content… as objects that can be modified.… The document object is the main “entry point” to the page.… BOM (Browser Object Model).The Browser Object Model (BOM) represents additional objects provided by the

Iterable objects are a generalization of arrays.… That’s a concept that allows us to make any object useable in a for..of loop.… But there are many other built-in objects, that are iterable as well.… Onward, for..of works only with that returned object.… So, the iterator object is separate from the object it iterates over.

), that is either null or references another object.… An object may not inherit from two others.… objects that inherit from it.… the state of the big object.… In JavaScript, all objects have a hidden [[Prototype]] property that’s either another object or null.

Web storage objects localStorage and sessionStorage allow to save key/value pairs in the browser.… Why additional objects?… Unlike cookies, web storage objects are not sent to server with each request.… Object-like access.We can also use a plain object way of getting/setting keys, like this:… Unfortunately, storage objects are not iterable.

In object-oriented programming, a class is an extensible program-code-template for creating objects,… So the object has access to class methods.… object any more.… Bind the method to object, e.g. in the constructor.… basis, there’s a separate function for each Button object, with this inside it referencing that object

Built-in methods like filter, map and others – return new objects of exactly the inherited type PowerArray… Their internal implementation uses the object’s constructor property for that.… For instance, Array extends Object.… Here’s the picture structure for Date and Object: As you can see… , there’s no link between Date and Object.

The two most used data structures in JavaScript are Object and Array.… Objects allow us to create a single entity that stores data items by key.… Object destructuring.The destructuring assignment also works with objects.… The left side contains an object-like “pattern” for corresponding properties.… Object properties that have no mapping are copied to the rest object.

Object store.To store something in IndexedDB, we need an object store.… An example of an object that can’t be stored: an object with circular references.… Such objects are not serializable. JSON.stringify also fails for such objects.… But when we store objects, IndexedDB allows setting up an object property as the key, which is much more… A cursor is a special object that traverses the object storage, given a query, and returns one key/value

A File object inherits from Blob and is extended with filesystem-related capabilities.… – is an array of Blob/BufferSource/String values. fileName – file name string. options – optional object… That’s how we can get a File object from <input type="file">:… ) objects.… Summary.File objects inherit from Blob.

They are supported for: Map Set Array Plain objects also support similar methods, but the syntax is… Remember, objects are a base of all complex structures in JavaScript.… So we may have an object of our own like data that implements its own data.values() method.… The second difference is that Object.* methods return “real” array objects, not just an iterable.… Use Object.fromEntries(array) on the resulting array to turn it back into an object.

First, the promise, returned by fetch, resolves with an object of the built-in Response class as soon… Response headers.The response headers are available in a Map-like headers object in response.headers.… JSON-encoded), FormData object, to submit the data as multipart/form-data, Blob/BufferSource to send… Sending an image.We can also submit binary data with fetch using Blob or BufferSource objects.… For Blob objects that type becomes the value of Content-Type.

That’s why dates have access to generic object methods.… When an object method runs, it gets the current object as this.… Now let’s add one more object to the chain.… That’s essential: all object methods get the current object as this, not a prototype or something.… When a function is specified as a class or object method, its [[HomeObject]] property becomes that object

Objects are just not meant for such use.… But at the core it’s still an object.… Array is an object and thus behaves like an object.… Let’s recall the rules: Two objects are equal == only if they’re references to the same object.… If one of the arguments of == is an object, and the other one is a primitive, then the object gets converted

As we know, objects can store properties.… But an object property is actually a more flexible and powerful thing.… and its property to apply the descriptor. descriptor Property descriptor object to apply.… Normally, a built-in toString for objects is non-enumerable, it does not show up in for..in.… the addition of new properties to the object.

By specification, only two primitive types may serve as object property keys: string type, or symbol… For instance, if we’re working with user objects, that belong to a third-party code.… The idea is that when we clone an object or merge objects, we usually want all properties to be copied… For instance, Symbol.toPrimitive allows us to describe object to primitive conversion.… Symbols have two main use cases: “Hidden” object properties.

When passing object methods as callbacks, for instance to setTimeout, there’s a known problem: “losing… Once a method is passed somewhere separately from the object – this is lost.… That’s because setTimeout got the function user.sayHi, separately from the object.… For example, for an object method. The native bind does not allow that.… Usually we apply bind to fix this for an object method, so that we can pass it somewhere.

Not talking about objects yet In this chapter, we won’t cover objects.… Later, after we learn about objects, in the chapter Object to primitive conversion we’ll see how objects… Objects aren’t covered here.… We’ll return to them later in the chapter Object to primitive conversion that is devoted exclusively… to objects after we learn more basic things about JavaScript.

Objects and Symbols.The object type is special.… Being that important, objects deserve a special treatment.… Here, it serves just as an example of an object. The result of typeof null is "object".… Functions belong to the object type.… For null returns "object" – this is an error in the language, it’s not actually an object.

In JavaScript we can only inherit from a single object.… There can be only one [[Prototype]] for an object. And a class may extend only one other class.… A mixin example.The simplest way to implement a mixin in JavaScript is to make an object with useful… An important feature of many browser objects (for instance) is that they can generate events.… So let’s make a mixin that allows us to easily add event-related functions to any class/object.

Object handlers: handleEvent.We can assign not just a function, but an object as an event handler using… The menu object only gets mousedown and mouseup here, not any other types of events.… Also addEventListener supports objects as event handlers.… No matter how you assign the handler – it gets an event object as the first argument.… That object contains the details about what’s happened.

Let’s meet a new built-in object: Date.… Creation.To create a new Date object call new Date() with one of the following arguments: new Date()… can always create a date from a timestamp using new Date(timestamp) and convert the existing Date object… Date and time in JavaScript are represented with the Date object.… We can’t create “only date” or “only time”: Date objects always carry both.

The idea is that we have an object, such as range here:… In other words, we want to add an iteration ability to the object.… To make an object iterable asynchronously: Use Symbol.asyncIterator instead of Symbol.iterator.… To iterate over such an object, we should use a for await (let item of iterable) loop.… This method must return the object with next() method returning a promise (2).

There’s a special built-in object for such purposes: AbortController.… A controller is an extremely simple object… could implement the same kind of event listening in our code on our own, without the AbortController object… But what’s valuable is that fetch knows how to work with the AbortController object.… AbortController is a simple object that generates an abort event on its signal property when the abort

This works (object dot method): This… The value of Reference Type is a three-value combination (base, name, strict), where: base is the object… When parentheses () are called on the Reference Type, they receive the full information about the object… That’s for the subsequent method call () to get the object and set this to it.… It only matters in subtle cases, such as when a method is obtained dynamically from the object, using

When the browser loads the page, it “reads” (another word: “parses”) the HTML and generates DOM objects… For element nodes, most standard HTML attributes automatically become properties of DOM objects.… For instance, if the tag is <body id="page">, then the DOM object has body.id="page… DOM nodes are regular JavaScript objects. We can alter them.… Properties – is what’s in DOM objects.

In the browser, there are additional higher-level objects, described in File API, in particular Blob.… consists of an optional string type (a MIME-type usually), plus blobParts – a sequence of other Blob objects… of a Blob, create new Blob objects from them, mix them into a new Blob and so on.… The mapping is automatically cleared on document unload, so Blob objects are freed then.… Performance and memory losses on big Blob objects for encoding.

The built-in TextDecoder object allows one to read the value into an actual JavaScript string, given… encoding, utf-8 by default, but big5, windows-1251 and many other are also supported. options – optional object… input – BufferSource to decode. options – optional object

The value of this in User.staticMethod() call is the class constructor User itself (the “object… methods are used to implement functions that belong to the class as a whole, but not to any particular object… For instance, we have Article objects and need a function to compare them.… Static methods aren’t available for individual objects… Static methods are callable on classes, not on individual objects.

The Lexical Environment object consists of two parts: Environment Record – an object that stores all… Lexical Environment is a specification object “Lexical Environment” is a specification object… We can’t get this object in our code and manipulate it directly.… As any JavaScript object, it’s only kept in memory while it’s reachable.… dies when it becomes unreachable (just like any other object).

A promise is a special JavaScript object that links the “producing code” and the “consuming code” together… The constructor syntax for a promise object is:… Reject with Error objects In case something goes wrong, the executor should call reject.… But it is recommended to use Error objects (or objects that inherit from Error).… Instead, it will create and return a Promise object that resolves when the loading is complete.

They can be passed around, used as objects, and now we’ll see how to forward calls between them and decorate… Using “func.call” for the context.The caching decorator mentioned above is not suited to work with object… As an example, in the code below we call sayHi in the context of different objects: sayHi.call(user)… and call it in the context of another object.… The alternative is to use rest parameters object that is a real array.