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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Iavascript.programowanie of inheritance is a great way to make a program into a big ugly mess. It returns a function like print which, instead of adding to the output, replaces its previous output.

JavaScript Programowanie obiektowe

This method gathers bugs, or other things that have an act method, and stores them in objects that javascript.programoanie contain their current position: Some actions require additional checking before they are executed, this is done with a separate if so that if a creature, for example, tries to walk through a wall, we javascriptp.rogramowanie not generate an “Unsupported action” exception.

That is exactly what we need for the onStep property. This way, if they ever want to change their object in such a way that it no longer has a length property, for example because it now javascript.programodanie some internal array whose length it must return, they can update the function without changing the interface.

This requires some discipline, but the result is a biotope that does not destroy itself. If no property is found, the value undefined is given. In fact there are, as usual, multiple good approaches to this.

Unfortunately, none of them is quite perfect. You give it the object on the left hand side, and a constructor on the right hand side, and it returns a boolean, true if the constructor’s prototype property is the direct or indirect prototype of the object, and false otherwise. It starts with an energy of 10and behaves in the following way:. Another good solution is to use a function similar to partial from chapter 6. This technique is called ‘ inheritance’.

Some problems are best solved by building a complex family tree of types. When an object does too much, it becomes a big mess of functionality, and a formidable source of confusion. This can be solved by doing something even uglier:. Each living thing in the terrarium gets a new property, energywhich is reduced by performing actions, and increased by eating things. For example, if there are different rabbits, the speak method must indicate which rabbit is speaking.

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The simple objects we have used so far are based on the most basic prototype, which is associated with the Object constructor. When it has an energy of 30 or more, and there is room near it, it reproduces. It calls this function for every point on the grid, giving it the point object for that point as its first argument, and the value that is on the grid at that point as second argument. One can use an array of arrays, like this:. If it is, it dies, and we remove it.

Still, Firefox is a widely used browser, so when you write a program for the web you have to be careful with this. This is easy to do, and in some cases it is the best solution, but in this case there is a cleaner way.

When it is running, step is automatically called every half second, so the bugs keep moving. Functions used to create new objects like this are called constructors. In chapter 7 we used three functions, pointaddPointsand samePoint to work with points. This can be solved by doing something even uglier: Some languages provide ways to explicitly declare certain methods and properties ‘private’, and make it an error to use them from outside the object.

Adding a getLength method which only contains return this. We could of course just type [“n”, “ne”, Lichen do not move, they just use photo-synthesis to gather energy, and reproduce.

Consider reading the third edition instead.

JavaScript. Programowanie obiektowe by Stoyan Stefanov on Apple Books

This allows us to have all kinds of bugs, without changing anything about the terrarium code. One can use an array of arrays, like this: Do not write out all the directions, use the each method on the directions dictionary. It is important to bear in mind that inheritance, in the end, is just a trick that allows lazy 3 programmers to write less code.

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. It returns a value that can be given to clearInterval to stop its effect. This will not work.

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If you have an object hedgehogwhich has the unique habit of rolling up when it is kicked, you can just change its kick method. Firstly toStringwhich converts the javascdipt.programowanie back to a string similar to the plan it was based on, so that you can see what is going on inside it. Each property holds a string of one character, as returned by characterFromElementjavascript.programowanle what the bug can see in that direction.

We could have used a single string, but because JavaScript strings must stay on a single line it would have been a lot harder to type. If you choose the right amount of turns for this hibernation, or have them wake up automatically when they smell lots of food, this could be a good strategy.

But to make the result readable, it would be nice to have a newline at the end of every row. This means that all simple objects have a toString method, which converts them to a string.

We could, for example, replace forEach and map with methods on arrays, and make the startsWith function we wrote in chapter 4 a method on strings. If there is no obuektowe property, or an invalid one, it leaves the variables target and valueAtTarget undefined. If there is a property that obiiektowe the name javascript.proramowanie are looking for, that is the value we get.

If there is no such property, it continues searching the prototype of the object, and then the prototype of the prototype, and so on. In this chapter, we will discuss these ideas, along with JavaScript’s rather eccentric take on them. On this grid there are a number of obiekgowe.

A function is called as a method when it is looked up as a property, and immediately called, as in object.