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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.

In maths, one would write xn = x * xn-1.… pow(2, 1).The process repeats: a new subcall is made at line 5, now with arguments x=2, n=1.… pow(2, 1).… It has the result of the subcall pow(2, 1), so it also can finish the evaluation of x * pow(x, n - 1)… Or an object with departments.

’s 9007199254740991), or less than -(253-1) for negatives.… Objects and Symbols.The object type is special.… 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.

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()… The date parameter is actually the day of month, if absent then 1 is assumed.… 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.

Here the flow is: The initial promise resolves in 1 second (*), Then the .then handler is called (**… So in the code above all alert show the same: 1.… So the output is the same as in the previous example: 1 → 2 → 4, but now with 1 second delay between… – an arbitrary object that has a method .then.… In the example above resolve(2) is called after 1 second (**).

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.… Move all elements to the left, renumber them from the index 1 to 0, from 2 to 1 and so on.… Let’s recall the rules: Two objects are equal == only if they’re references to the same object.

Fine for objects.… Starting from the index 1 it removed 1 element.… So the function result is 1.… 1 the second call 1 2 3 the third call 3 3 6 the fourth call 6 4 10 the fifth call 10 5 15… They are based on objects.

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… Numeric conversion rules: Value Becomes… undefined NaN null 0 true and false 1… Objects aren’t covered here.… to objects after we learn more basic things about JavaScript.

And it can’t be both version 1 and 2.… 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

-(253-1), as we mentioned earlier in the chapter Data types.… -1 -1 -1.5 -2 -1 -1 -1 -1.6 -2 -1 -2 -1 These functions cover all of the possible ways to deal… It is one divided by ten 1/10, one-tenth.… A few examples: Math.random() Returns a random number from 0 to 1 (not including 1).… the docs for the Math object.

For instance, the Promise.all below settles after 3 seconds, and then its result is an array [1, 2, 3… But if any of those objects is not a promise, it’s passed to the resulting array “as is”.… For instance, here the results are [1, 2, 3]:… For instance, here the result will be 1:… for failed promises are available in the errors property of the AggregateError object.

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 iterate over such an object, we should use a for await (let item of iterable) loop.… asynchronously iterable, it must have a method Symbol.asyncIterator (1).… 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

By specification, only two primitive types may serve as object property keys: string type, or symbol… So that obj[1] is the same as obj["1"], and obj[true] is the same as obj["true"].… 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… Symbols have two main use cases: “Hidden” object properties.

The “arguments” variable.There is also a special array-like object named arguments that contains all… Arrow functions do not have "arguments" If we access the arguments object from… Now we know they don’t have the special arguments object either.… And surely we can’t manually list items in the code Math.max(arr[0], arr[1]… Note that it is possible to do the same thing to make a copy of an object:

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.

They can be passed around, used as objects, and now we’ll see how to forward calls between them and decorate… Append glue and this[1]. Append glue and this[2]. …Do so until this.length items are glued.… So, technically it takes this and joins this[0], this[1] …etc together.… and call it in the context of another object.… The alternative is to use rest parameters object that is a real array.

The underlying Range and Selection objects are easy to grasp, and then you’ll need no recipes to make… objects.… Selection.Range is a generic object for managing selection ranges.… As we know, Range objects always have their start before the end.… object, that we can insert elsewhere.

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

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

For all built-in errors, the error object has two main properties: name Error name.… We can use them to create error objects as well.… In the catch (err) {...} block we analyze the error object err.… And then enter -1 – there will be an immediate error, and the execution will take 0ms.… If an error object is not needed, we can omit it by using catch { instead of catch (err) {.

We can create Event objects like this:… options – the object with two optional properties: bubbles: true/false – if true, then the event bubbles… Technically we could live without, because we can assign any properties into a regular new Event object… The output order becomes: 1 → 2 → nested.… Summary.To generate an event from code, we first need to create an event object.

Connection status: readyState.The EventSource object has readyState property, that has one of three values… : When an object is created, or the… Event types.By default EventSource object generates three events: message – a message received, available… Resultserver.jsindex.htmlSummary.EventSource object automatically establishes a persistent connection… (=0), EventSource.OPEN (=1) or EventSource.CLOSED (=2). lastEventId The last received id.

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.

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.

For instance, this function returns a resolved promise with the result of 1; let’s test it:… Here’s an example with a promise that resolves in 1 second:… await accepts “thenables” Like promise.then, await allows us to use thenable objects… The idea is that a third-party object may not be a promise, but promise-compatible: if it supports .then… If await gets a non-promise object

Instead it returns a special object, called “generator object”, to manage the execution.… The result of next() is always an object with two properties: value: the yielded value. done: true if… If we do them, they return the same object: {done: true}.… …But please note: the example above shows 1, then 2, and that’s all. It doesn’t show 3!… And, surely, they are great for making iterable objects.

The x axis is the time: 0 – the start, 1 – the end of transition-duration.… That can be specified by the curve cubic-bezier(0, 0, 1, 1).… The linear is a shorthand for cubic-bezier(0, 0, 1, 1) – a straight line, which we described above.… The y is out of the “standard” range 0..1.… That is, the animation starts immediately and takes 1 step.

There are 3 differences from match: It returns an iterable object with matches instead of an array.… If there are no results, it returns an empty iterable object instead of null.… str.search(regexp).The method str.search(regexp) returns the position of the first match or -1… part of the string before the match $' inserts a part of the string after the match $n if n is a 1-… groups (if there are any), offset – position of the match, input – the source string, groups – an object

At index 1: the contents of the first parentheses.… The first group is returned as result[1]. Here it encloses the whole tag content.… If there are no matches, it returns not null, but an empty iterable object.… We can’t get the match as results[0], because that object is a pseudoarray.… Instead, it returns an iterable object, without the results initially.

Objects of that class are never created.… Objects of Node class are never created.… For example, let’s consider the DOM object for an <input> element.… , so “plain object” methods like hasOwnProperty are also available.… For JavaScript objects these commands usually do the same.

And so on upwards till the document object.… Normally it goes upwards till <html>, and then to document object, and some events even reach window… Also we can write our data into the event object in one handler and read it in another one, so we can… Here’s the picture, taken from the specification, of the capturing (1), target (2) and bubbling (3) phases… Each handler can access event object properties: event.target – the deepest element that originated

HttpError objects may have a statusCode property with a value like 404 or 403 or 500.… But if we inherit, then it becomes possible to use obj instanceof Error to identify error objects.… The ReadError object will keep the reference to the original error in its cause property.… It is widely used in object-oriented programming. Summary.… But sometimes we have an error object coming from a 3rd-party library and there’s no easy way to get

like CSS-property transition-timing-function that gets the fraction of time that passed (0 at start, 1… The value progress=0 denotes the beginning animation state, and progress=1 – the end state.… Regular bounce – the object bounces at the bottom, then at the end sharply jumps to the top.… Gets a time fraction from 0 to 1, returns the animation progress, usually from 0 to 1. draw – the function

XMLHttpRequest is a built-in browser object that allows to make HTTP requests in JavaScript.… travels them in the order 0 → 1 → 2 → 3 → … → 3 → 4.… So, if we want to get an object with name/value pairs, we need to throw in a bit JS.… It can send almost any body, including Blob and BufferSource objects.… There’s another object, without methods, exclusively to track upload events: xhr.upload.

Step 1.… 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.… dies when it becomes unreachable (just like any other object).

The basic binary object is ArrayBuffer – a reference to a fixed-length contiguous memory area.… To access individual bytes, another “view” object is needed, not buffer[index].… To manipulate an ArrayBuffer, we need to use a “view” object.… A view object does not store anything on its own.… ArrayBuffer is the core object, the root of everything, the raw binary data.

In JavaScript, they are available via the RegExp object, as well as being integrated in methods of strings… There are two syntaxes that can be used to create a regular expression object.… part of the string before the match $' inserts a part of the string after the match $n if n is a 1-

All importers get exactly the one and only admin object:… As you can see, when 1.js changes the name property in the imported admin, then 2… Then it can export a configuration object expecting the outer code to assign to it.… Compare it to non-module scripts, where this is a global object:… So we’ll see undefined first, and then object.

According to the Document Object Model (DOM), every HTML tag is an object.… The text inside a tag is an object as well.… All these objects are accessible using JavaScript, and we can use them to modify the page.… For example, document.body is the object representing the <body> tag.… Every tree node is an object.

empty” or “does not exist”, undefined – a type with a single value undefined, meaning “not assigned”, object… Later we’ll study more types of loops to deal with objects.… Parameters can have default values: function sum(a = 1, b = 2) {...}.

, not anyElem.getElementById The method getElementById can be called only on document object… As of now, its length is 1.… If we use it instead, then both scripts output 1:

The global object provides variables and functions that are available anywhere.… Using for polyfills.We use the global object to test for support of modern language features.… 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.

DOMContentLoaded.The DOMContentLoaded event happens on the document object.… s actually the delay until the DOMContentLoaded event. window.onload.The load event on the window object… but also forms and other formats, as described in the chapter Fetch, but usually it’s a stringified object… The typical output: [1] initial readyState:loading [2] readyState:interactive [2] DOMContentLoaded [

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].

WebSocket objects are cross-origin by nature. There are no special headers or other limitations.… set by socket.binaryType property, it’s "blob" by default, so binary data comes as Blob objects… Blob is a high-level binary object, it directly integrates with <a>, <img> and other tags… socket.readyState property with values: 0 – “CONNECTING”: the connection has not yet been established, 1