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Some problems are best solved by building a complex family tree of types. Each property holds a string of one character, as returned by characterFromElementindicating what the bug can see in that direction.
Unfortunately, when a program starts to make serious use of inheritance, this approach to objects quickly becomes clumsy. You have to take care not to get too inheritance-happy, though. Note that the action function is called with both the name of the property and the value it has in the object. Fortunately, this terrarium-simulator is not required to be accurate in any way, so we can get away with it. Every object has a method called hasOwnPropertywhich tells us whether the object has a property with a given name.
Because they share these traits, the terrarium can approach them in the same way. It will be stored in the object, and the next time we want to go over the collection of cats, calling object. Every object is based on a prototype, which gives it a set of inherent properties. Calling a function always results in a new this being defined inside that function, even when it is not used as a method. In chapter 7 we used three functions, pointaddPointsand samePoint to work with points.
The name self or that is often used for such a variable.
For that second problem, this page conveniently provides a function called inPlacePrinter. It would be nice if part of this could be moved into another object, so that the terrarium object itself doesn’t get too big and complex. A trick similar to the clone function can be used to get around it: A function is called as a method when it is looked up as a property, and immediately called, as in object.
If there is no direction property, or an invalid one, it leaves the variables target and valueAtTarget undefined. It starts with an energy of 10and behaves in the following way:. Unfortunately, none of them is quite perfect. This method looks up the character associated with a constructor, and stores it in the dictionary.
It would be nicer if it would print automatically.
The terrarium merely provides the infrastructure that asks them what to do every half second, and if they decide to move, it makes sure this happens. To prevent wasting your time, it is advisable to document your interfaces only after they have been used in a few real situations and proven themselves to be practical.
When it needs to do any ‘constructing’ work, this is done by a method called construct. You can use a constructor’s prototype property to get access to, well, their prototype: After all, we could have simply written this:.
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. For this reason, some people prefer not to touch these prototypes at all. First, its constructor, which takes a plan an array of strings as argument, and initialises its grid.
Firstly, having a small, clearly described interface makes an object easier to use.
Code which uses point objects may freely retrieve and modify x and y. Instead, I will show a very simple approach which suffices in most cases. Here is a new approach jaascript.programowanie the Rabbit constructor: