programming
When we write our code using objects to represent entities, that’s called object-oriented… programming, in short: “OOP”.… “this” is not bound.In JavaScript, keyword this behaves unlike most other programming languages.… Usually such call is a programming error.… The consequences of unbound this
If you come from another programming language, then you
In object-oriented programming, a class is an extensible program-code-template for creating objects,… there’s a more advanced “class” construct, that introduces great new features which are useful for object-oriented… programming.… object any more.… basis, there’s a separate function for each Button object, with this inside it referencing that object
One of the most important principles of object oriented programming – delimiting internal interface from… As we’ll see, in programming objects are like coffee machines.… Internal and external interface.In object-oriented programming, properties and methods are split into… The same in programming.… Supportable
The situation in programming is more complex than with a real-life coffee machine, because
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.… 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.… Summary.Mixin – is a generic object-oriented programming term: a class that contains methods for other
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
JavaScript is a very function-oriented language. It gives us a lot of freedom.… 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.… Closure
There is a general programming term “closure”, that developers generally should know
The device orientation changed (tablet rotated).… The user may even drag the ball image out of the browser, into their Mail program or a File Manager.… Nevertheless, coordinate properties of the event objects, such as clientX/clientY will still be correct
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.
One of the fundamental differences of objects versus primitives is that objects are stored and copied… Objects are not like that.… Comparison by reference.Two objects are equal only if they are the same object.… very rarely – usually they appear as a result of a programming mistake.… object.
Unlike some other programming languages, such as Ruby or C++, we can’t implement a special object method… 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].
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.
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.
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.
For example:
When the program fully terminates its operation (for example, when closing a tab in a browser… updated implementation is that finalizers allow parallel processes to be created between the “main” program… In the context of JavaScript, the “main” program – is our JavaScript-code, that runs and executes in… It is important to understand that during this time gap, the main program can make any changes to the… the cleanup callback, we must check to see if an entry has been added back to the cache by the main program
In programming, we often want to take something and extend it.… In programming, this is called “prototypal inheritance”.… 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.
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.… objects created by new F will have another object as [[Prototype]], but already existing objects keep… Later we’ll see more advanced programming patterns that rely on it.… The value of F.prototype should be either an object or null: other values won’t work.
No matter how great we are at programming, sometimes our scripts have errors.… We can use them to create error objects as well.… Like a programming error (variable is not defined) or something else, not just this “incorrect data”… Like a programming error or some other terrible thing.
Is there a way to react on such occurrences?… window.onerror is usually not to recover the script execution – that’s probably impossible in case of programming
That may be useful for advanced programming patterns when we use functions to generate classes depending… Advanced note
This note assumes you have a certain experience with classes, maybe in other programming… behavior when we access an overridden field in parent constructor, quite different from most other programming… When an object method runs, it gets the current object as this.… That’s essential: all object methods get the current object as this, not a prototype or something.
is a safe way to access nested object properties, even if an intermediate property doesn’t exist.… As an example, let’s say we have user objects that hold the information about our users.… In Web development, we can get an object that corresponds to a web page element using a special method… Then, if user happens to be undefined, we’ll see a programming error about it and fix it.… So that it won’t hide programming errors from us, if they occur.
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.… In modern programming, there is only one case where modifying native prototypes is approved.… The object itself stores only the data (array items, object properties, the date)
Primitives also store
Objects are just not meant for such use.… Some programming languages allow the use of negative indexes for the same purpose, like fruits[-1].… Array is an object and thus behaves like an object.… Don’t compare arrays with ==.Arrays in JavaScript, unlike some other programming… Let’s recall the rules:
Two objects are equal == only if they’re references to the same object.
If you are not new to programming, then it is probably familiar and you could skip this chapter.… Recursion is a programming pattern that is useful in situations when a task can be naturally split into… The 2nd case when we get an object is the recursive step.… Or an object with departments.… Summary.Terms:
Recursion is a programming term that means calling a function from itself.
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… 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.… JSON is a data format that has its own independent standard and libraries for most programming languages
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.… 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… If you are familiar with low-level programming, more detailed information about V8’s garbage collector
For example, a programming error:… an error occurs, and there’s no .catch, the unhandledrejection handler triggers, and gets the event object… handler should analyze errors (custom error classes help) and rethrow unknown ones (maybe they are programming
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… That sounds like Ruby
In some programming languages, like Ruby, there’s a single symbol per… Symbols have two main use cases:
“Hidden” object properties.
– an arbitrary object that has a method .then.… The idea is that 3rd-party libraries may implement “promise-compatible” objects of their own.… Here’s an example of a thenable object:… This feature allows us to integrate custom objects with promise chains without having to inherit from… Bigger example: fetch.In frontend programming, promises are often used for network requests.
a string and then store a number:
Programming… 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.
The programs in this language are called scripts.… execute not only in the browser, but also on the server, or actually on any device that has a special program… Modern JavaScript is a “safe” programming language.… JavaScript on a webpage may not read/write arbitrary files on the hard disk, copy them or execute programs… Kotlin is a modern, concise and safe programming language that can target the browser or Node.
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}.… And, surely, they are great for making iterable objects.… In web-programming we often work with streamed data, so that’s another very important use case.
This is a real-life analogy for things we often have in programming:
A “producing code” that does something… 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:… 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.
Using “eval”.In modern programming eval is used very sparingly.… Using outer local variables inside eval is also considered a bad programming practice, as it makes maintaining
MutationObserver is a built-in object that observes a DOM element and fires a callback when it detects… attach it to a DOM node:
config is an object… changes, the callback is executed: changes are passed in the first argument as a list of MutationRecord objects… MutationRecord objects have properties:
type – mutation type, one of
"attributes": attribute… Let’s say we’re making a website about programming.
When the regexp engine (program module that implements searching for regexps) comes across \b, it checks
vertical line symbols:
In classical programming… ampersands &&:
In classical programming
For instance, we need to find programming languages: HTML, PHP, Java or JavaScript.
is that before JavaScript is published to production, it’s compressed using a minifier – a special program
One of common tasks for regexps is “lexical analysis”: we get a text, e.g. in a programming language,
Functional languages
It’s interesting to note that there exist so-called pure functional programming… Variable naming is one of the most important and complex skills in programming.
The “script” tag.JavaScript programs can be inserted almost anywhere into an HTML document using the
Comments.As time goes on, programs become more and more complex.
limitation is surely debatable, it was added to the language specification with the purpose to avoid programming
At first sight, commenting might be obvious, but novices in programming often use them wrongly.
Not only JavaScript
The same issue exists in many other programming languages.… Other math functions.JavaScript has a built-in Math object… There are more functions and constants in Math object, including trigonometry, which you can find in… the docs for the Math object.… More mathematical functions:
See the Math object when you need them.
That is: if a script loaded successfully, then onload triggers, even if it has programming errors in
That’s called a “callback-based” style of asynchronous programming
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.
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