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author Radomir Dopieralski <radomir.dopieralski@allegro.pl>
date Wed, 27 Jun 2012 16:35:54 +0200
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1 Simple classes
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2 ==============
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3
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4 JavaScript has objects, which through the object tree support
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5 inheritance. Almost all object-oriented languages have classes and
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6 instances, but JavaScript has neither. This will be explained later,
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7 along with a discussion of the consequences.
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8
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9 For now our focus is on getting going with object-oriented
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10 programming. The easiest way to do this is via ``create``.
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13 Definition
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14 ----------
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15
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16 Here's a factory function that creates classes. It returns a function
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17 called ``cls``, which in turn when called returns instances. At it's
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18 heart is ``create``, and also ``apply`` and ``arguments``, which we've not
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19 seen before).
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20
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21 .. literalinclude:: /core-javascript-work/library.js
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22 :language: javascript
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23 :start-after: start SimpleClass
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24 :end-before: end SimpleClass
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25
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26
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27 Why *cls*?
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28 ----------
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29
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30 We call the returned function *cls* because in JavaScript *class*,
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31 like *function* is a reserved word in JavaScript. However, in
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32 JavaScript the identifier *class* has no meaning, and cannot be used
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33 in any valid JavaScript program. It seems that they intended to
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34 provide a built-in class capability, but never got round to it.
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37 Fruit example
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38 -------------
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39
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40 Here's an example of the use of ``SimpleClass``. There's a bug in it,
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41 and I've changed the test so it passes. Can you find the bug and fix
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42 the example?
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43
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44 .. literalinclude:: /core-javascript-work/test_library.js
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45 :language: javascript
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46 :start-after: start SimpleClass
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47 :end-before: end SimpleClass