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JAVASCRIPT.PROGRAMOWANIE OBIEKTOWE PDF

JS programowanie obiektowe. 1. JavaScript Programowanie Obiektowe Piotr Czajkowski [email protected]; 2. constructor new. Poznasz i zrozumiesz najnowsze mechanizmy JS (ES6+) Programowanie obiektowe z użyciem słów kluczowych class, extends itd. In the early nineties, a thing called object-oriented programming stirred up the software industry. Most of the ideas behind it were not really new at the time, but.

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In fact there are, as usual, multiple good approaches to this. It is possible to write a function that does this, though, by using the following trick:. But I javascript.programoawnie that can wait until we need it. It would also look better if, instead of printing a thousand terraria below each other, we could update a single printout of the terrarium.

JavaScript. Programowanie obiektowe

Personally, I treat writing documentation as a ‘finishing touch’ to add to a system. An expression such as this one can be used to reliably work around this:. JavaScript does not allow an object to have multiple prototypes, and even if it did, the problem would not be quite that easy to solve. If there is a property that has the name we are looking javascript.progrsmowanie, that javascript.prograomwanie the value we get.

If you rewrite the constructor, do not forget to re-register it in the creatureTypes dictionary, or the terrarium will continue to use the old constructor.

JavaScript does not, so you will have to rely on comments to describe the interface to an object. For now, it only knows about the “move” action:.

And if, at some point, you find that you really need it, you can search the web, do some research, and figure out an approach that works obiektwoe your situation. After all, we could have simply written this:. A related problem is that it can often be practical to extend the prototypes of standard constructors such as Object and Array with new useful functions. Firstly, having a small, clearly described interface makes an object easier to use. Give the prototype of this constructor a method addwhich takes another point obisktowe argument and returns a new point whose x and y are the sum of the x and y of the two given points.

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Right now it contains three cases which are typed in directly, or ‘hard-coded’: If, for example, we javascript.programowaniee whether there is a cat called “constructor”we would have checked it like this: When a function is called with the word javascript.programowaniee in front of it, its this variable will point at a new object, which it will automatically return unless it explicitly returns something else.

We also provide a convenient shorthand for this, an extend method, which clones the object it is applied to and adds to this clone the properties javascript.proramowanie the object that it is given as an argument.

JavaScript. Programowanie obiektowe by Stoyan Stefanov on Apple Books

We already saw simple examples of this, like the toString method on objects. Quite a few times, I have found myself accidentally adding methods to a constructor instead of its prototype, or trying to call Array. By remembering the last direction it went, and preferring that direction, the eater will waste less time, and find food faster. In most cases, this means the new type will still support the interface of the old type, though it might also javacsript.programowanie a few methods javascript.rpogramowanie the old type does not have.

Objects are turned to strings by calling their toString method, so giving your own object types a meaningful toString is a good way to make them readable when printed out.

All objects that have a meaningful toString method can be given to javascrippt.programowanie and javascript.programlwanie functions that need to convert values to strings, and the correct string will be produced, no matter how their toString method chooses to build this string. Unless someone actually messes with the method in Object. For example, we could give all objects a method called propertieswhich returns an array with the names of the non-hidden properties that the object has: For each of the eight directions, it contains a property.

JavaScript Programowanie obiektowe

If we make the old prototype object the prototype of the new prototype object you may have to re-read that a few timesit will automatically have all its properties.

When the act method is called, it is given an object javascript.progrramowanie information about the surroundings of the bug in question.

This is easy to do, and in some cases javascript.prrogramowanie is the best solution, but in this case there is a cleaner way. When a process is hard and confusing, people are always on the lookout for a magic solution. Do not write out all the directions, use the each method on the directions dictionary.

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We could go over the properties of Terrarium.

Consider reading the third edition instead. The name self or that is often used for such a variable. All of a sudden, everybody was extolling the virtues of object-orientation, enthusiastically applying it to every problem, convincing themselves they had finally found the right way to write programs.

Unfortunately, none of them is quite perfect.

Justyna Walkowska (Translator of JavaScript. Programowanie obiektowe)

javascipt.programowanie It has to define some kind of representation, ways to access this representation, a way to initialise the grid from a ‘plan’ array, a way to write the content of the grid to a string for the toString method, and the movement of the bugs on the grid.

We use a ‘fake constructor’, and apply instanceof to it.

By always picking a random direction, it will often move back and forth without getting anywhere. This technique is called ‘ inheritance’.

This way, if we decide for some reason to use a different method for storing the values, we only have to rewrite valueAt and setValueAtand the other methods can stay untouched. It takes one argument, the point at which javascript.programowanif bug is currently standing, and returns an object with information about the surroundings of that point.

This object keeps track of the shape and content of the terrarium, and lets the bugs inside move. Earlier, I mentioned that javascript.provramowanie terrarium will ask the bugs what action they want to take.

Obuektowe, the question of whether inheritance is being used correctly boils down to the question of whether the resulting code works correctly and avoids useless repetitions.

That is exactly what we need for the onStep property. This makes it easy to distinguish them from other functions.