js4py: core-javascript/object-tree.rst annotate

annotate core-javascript/object-tree.rst @ 213:0ea90a1819c2 default tip

Custom theming

author	Radomir Dopieralski <radomir.dopieralski@allegro.pl>
date	Wed, 27 Jun 2012 16:35:54 +0200
parents	29c7fe19aeb5
children

rev	line source
102 29e156f97bfb More or less done with object-tree.rst. jf3243 parents: 101 diff changeset	1 The object tree
29e156f97bfb More or less done with object-tree.rst. jf3243 parents: 101 diff changeset	2 ===============
3 65872f01ea89 inheritance.rst: Made a start on this page. Jonathan Fine <jfine@pytex.org> parents: diff changeset	3
102 29e156f97bfb More or less done with object-tree.rst. jf3243 parents: 101 diff changeset	4 Objects can have attributes. The statements
3 65872f01ea89 inheritance.rst: Made a start on this page. Jonathan Fine <jfine@pytex.org> parents: diff changeset	5
102 29e156f97bfb More or less done with object-tree.rst. jf3243 parents: 101 diff changeset	6 .. code-block:: javascript
3 65872f01ea89 inheritance.rst: Made a start on this page. Jonathan Fine <jfine@pytex.org> parents: diff changeset	7
102 29e156f97bfb More or less done with object-tree.rst. jf3243 parents: 101 diff changeset	8 value = obj.attr # Get the attr of 'a'.
29e156f97bfb More or less done with object-tree.rst. jf3243 parents: 101 diff changeset	9 obj.attr = value # Set the attr of 'a'.
3 65872f01ea89 inheritance.rst: Made a start on this page. Jonathan Fine <jfine@pytex.org> parents: diff changeset	10
207 29c7fe19aeb5 Mark inline code using duble backticks Radomir Dopieralski <radomir.dopieralski@allegro.pl> parents: 204 diff changeset	11 respectively set and get the ``attr`` attribute of the object
204 45e7d5e8fa97 Use double backticks for inline code Radomir Dopieralski <radomir.dopieralski@allegro.pl> parents: 117 diff changeset	12 ``obj``. Inheritance is where an object gets some its attributes from
102 29e156f97bfb More or less done with object-tree.rst. jf3243 parents: 101 diff changeset	13 one or other more objects. JavaScript uses an object tree for
29e156f97bfb More or less done with object-tree.rst. jf3243 parents: 101 diff changeset	14 inheritance.
5 48d5ba601286 inheritance.rst: Finished, at least for this draft. Jonathan Fine <jfine@pytex.org> parents: 3 diff changeset	15
8 62b9c15e287f classes.rst: Finished first draft. Jonathan Fine <jfine@pytex.org> parents: 5 diff changeset	16
62b9c15e287f classes.rst: Finished first draft. Jonathan Fine <jfine@pytex.org> parents: 5 diff changeset	17 .. _inheritance-tree:
62b9c15e287f classes.rst: Finished first draft. Jonathan Fine <jfine@pytex.org> parents: 5 diff changeset	18
3 65872f01ea89 inheritance.rst: Made a start on this page. Jonathan Fine <jfine@pytex.org> parents: diff changeset	19 Tree
65872f01ea89 inheritance.rst: Made a start on this page. Jonathan Fine <jfine@pytex.org> parents: diff changeset	20 ----
65872f01ea89 inheritance.rst: Made a start on this page. Jonathan Fine <jfine@pytex.org> parents: diff changeset	21
102 29e156f97bfb More or less done with object-tree.rst. jf3243 parents: 101 diff changeset	22 All JavaScript objects are part of an inheritance tree. Each object
29e156f97bfb More or less done with object-tree.rst. jf3243 parents: 101 diff changeset	23 in the tree has a parent object, which is also called the prototype
29e156f97bfb More or less done with object-tree.rst. jf3243 parents: 101 diff changeset	24 object (of the child). There is a single exception to this rule,
29e156f97bfb More or less done with object-tree.rst. jf3243 parents: 101 diff changeset	25 which is the root of the tree. The root of the tree does not have
29e156f97bfb More or less done with object-tree.rst. jf3243 parents: 101 diff changeset	26 a parent object.
5 48d5ba601286 inheritance.rst: Finished, at least for this draft. Jonathan Fine <jfine@pytex.org> parents: 3 diff changeset	27
102 29e156f97bfb More or less done with object-tree.rst. jf3243 parents: 101 diff changeset	28 .. note::
29e156f97bfb More or less done with object-tree.rst. jf3243 parents: 101 diff changeset	29
29e156f97bfb More or less done with object-tree.rst. jf3243 parents: 101 diff changeset	30 **You can't get far in JavaScript without understanding the
29e156f97bfb More or less done with object-tree.rst. jf3243 parents: 101 diff changeset	31 object tree.**
29e156f97bfb More or less done with object-tree.rst. jf3243 parents: 101 diff changeset	32
5 48d5ba601286 inheritance.rst: Finished, at least for this draft. Jonathan Fine <jfine@pytex.org> parents: 3 diff changeset	33
48d5ba601286 inheritance.rst: Finished, at least for this draft. Jonathan Fine <jfine@pytex.org> parents: 3 diff changeset	34 Get
48d5ba601286 inheritance.rst: Finished, at least for this draft. Jonathan Fine <jfine@pytex.org> parents: 3 diff changeset	35 ^^^
48d5ba601286 inheritance.rst: Finished, at least for this draft. Jonathan Fine <jfine@pytex.org> parents: 3 diff changeset	36
48d5ba601286 inheritance.rst: Finished, at least for this draft. Jonathan Fine <jfine@pytex.org> parents: 3 diff changeset	37 When JavaScript needs to get an attribute value of an object, it first
204 45e7d5e8fa97 Use double backticks for inline code Radomir Dopieralski <radomir.dopieralski@allegro.pl> parents: 117 diff changeset	38 looks up the name of the attribute in the object's dictionary. If the
45e7d5e8fa97 Use double backticks for inline code Radomir Dopieralski <radomir.dopieralski@allegro.pl> parents: 117 diff changeset	39 attribute name is a key in the dictionary, the associated value is returned.
5 48d5ba601286 inheritance.rst: Finished, at least for this draft. Jonathan Fine <jfine@pytex.org> parents: 3 diff changeset	40
204 45e7d5e8fa97 Use double backticks for inline code Radomir Dopieralski <radomir.dopieralski@allegro.pl> parents: 117 diff changeset	41 If the name is not a key, then the process is repeated using the
5 48d5ba601286 inheritance.rst: Finished, at least for this draft. Jonathan Fine <jfine@pytex.org> parents: 3 diff changeset	42 object's parent, grandparent, and so on until the key is found. If
204 45e7d5e8fa97 Use double backticks for inline code Radomir Dopieralski <radomir.dopieralski@allegro.pl> parents: 117 diff changeset	43 the key is not found in this way then ``undefined`` is returned.
102 29e156f97bfb More or less done with object-tree.rst. jf3243 parents: 101 diff changeset	44
5 48d5ba601286 inheritance.rst: Finished, at least for this draft. Jonathan Fine <jfine@pytex.org> parents: 3 diff changeset	45
102 29e156f97bfb More or less done with object-tree.rst. jf3243 parents: 101 diff changeset	46 Set
29e156f97bfb More or less done with object-tree.rst. jf3243 parents: 101 diff changeset	47 ^^^
5 48d5ba601286 inheritance.rst: Finished, at least for this draft. Jonathan Fine <jfine@pytex.org> parents: 3 diff changeset	48
48d5ba601286 inheritance.rst: Finished, at least for this draft. Jonathan Fine <jfine@pytex.org> parents: 3 diff changeset	49 When JavaScript needs to set an attribute value of an object it
48d5ba601286 inheritance.rst: Finished, at least for this draft. Jonathan Fine <jfine@pytex.org> parents: 3 diff changeset	50 ignores the inheritance tree. It simply sets that value in the
102 29e156f97bfb More or less done with object-tree.rst. jf3243 parents: 101 diff changeset	51 object's dictionary.
29e156f97bfb More or less done with object-tree.rst. jf3243 parents: 101 diff changeset	52
5 48d5ba601286 inheritance.rst: Finished, at least for this draft. Jonathan Fine <jfine@pytex.org> parents: 3 diff changeset	53
48d5ba601286 inheritance.rst: Finished, at least for this draft. Jonathan Fine <jfine@pytex.org> parents: 3 diff changeset	54 Root
48d5ba601286 inheritance.rst: Finished, at least for this draft. Jonathan Fine <jfine@pytex.org> parents: 3 diff changeset	55 ----
48d5ba601286 inheritance.rst: Finished, at least for this draft. Jonathan Fine <jfine@pytex.org> parents: 3 diff changeset	56
48d5ba601286 inheritance.rst: Finished, at least for this draft. Jonathan Fine <jfine@pytex.org> parents: 3 diff changeset	57 When the interpreter starts up, the root of the tree is placed at
204 45e7d5e8fa97 Use double backticks for inline code Radomir Dopieralski <radomir.dopieralski@allegro.pl> parents: 117 diff changeset	58 `Object.prototype`. (We'll find out later why that location is used.)
3 65872f01ea89 inheritance.rst: Made a start on this page. Jonathan Fine <jfine@pytex.org> parents: diff changeset	59
12 4be9f1bf2fd3 Reviewed and revised existing pages, and added some new stub pages. Jonathan Fine <jfine@pytex.org> parents: 8 diff changeset	60 Every object inherits from the root, although perhaps not
102 29e156f97bfb More or less done with object-tree.rst. jf3243 parents: 101 diff changeset	61 directly. Here's a simple example:
3 65872f01ea89 inheritance.rst: Made a start on this page. Jonathan Fine <jfine@pytex.org> parents: diff changeset	62
65872f01ea89 inheritance.rst: Made a start on this page. Jonathan Fine <jfine@pytex.org> parents: diff changeset	63 .. code-block:: javascript
65872f01ea89 inheritance.rst: Made a start on this page. Jonathan Fine <jfine@pytex.org> parents: diff changeset	64
65872f01ea89 inheritance.rst: Made a start on this page. Jonathan Fine <jfine@pytex.org> parents: diff changeset	65 js> root = Object.prototype
65872f01ea89 inheritance.rst: Made a start on this page. Jonathan Fine <jfine@pytex.org> parents: diff changeset	66 js> a = {}
102 29e156f97bfb More or less done with object-tree.rst. jf3243 parents: 101 diff changeset	67 js> a.attr === undefined
3 65872f01ea89 inheritance.rst: Made a start on this page. Jonathan Fine <jfine@pytex.org> parents: diff changeset	68 true
102 29e156f97bfb More or less done with object-tree.rst. jf3243 parents: 101 diff changeset	69 js> root.attr = 'gotcha'
29e156f97bfb More or less done with object-tree.rst. jf3243 parents: 101 diff changeset	70 js> a.attr
3 65872f01ea89 inheritance.rst: Made a start on this page. Jonathan Fine <jfine@pytex.org> parents: diff changeset	71 gotcha
65872f01ea89 inheritance.rst: Made a start on this page. Jonathan Fine <jfine@pytex.org> parents: diff changeset	72
207 29c7fe19aeb5 Mark inline code using duble backticks Radomir Dopieralski <radomir.dopieralski@allegro.pl> parents: 204 diff changeset	73 If we give root a ``attr`` attribute then every other object,
102 29e156f97bfb More or less done with object-tree.rst. jf3243 parents: 101 diff changeset	74 including those already created and those not yet created, also has a
207 29c7fe19aeb5 Mark inline code using duble backticks Radomir Dopieralski <radomir.dopieralski@allegro.pl> parents: 204 diff changeset	75 ``attr`` attribute with the same value. (In practice it's better not to
29c7fe19aeb5 Mark inline code using duble backticks Radomir Dopieralski <radomir.dopieralski@allegro.pl> parents: 204 diff changeset	76 change ``Object.prototpye``.)
102 29e156f97bfb More or less done with object-tree.rst. jf3243 parents: 101 diff changeset	77
29e156f97bfb More or less done with object-tree.rst. jf3243 parents: 101 diff changeset	78 This applies arrays:
3 65872f01ea89 inheritance.rst: Made a start on this page. Jonathan Fine <jfine@pytex.org> parents: diff changeset	79
102 29e156f97bfb More or less done with object-tree.rst. jf3243 parents: 101 diff changeset	80 .. code-block:: javascript
29e156f97bfb More or less done with object-tree.rst. jf3243 parents: 101 diff changeset	81
29e156f97bfb More or less done with object-tree.rst. jf3243 parents: 101 diff changeset	82 js> array = [0, 1, 2]
29e156f97bfb More or less done with object-tree.rst. jf3243 parents: 101 diff changeset	83 0,1,2
29e156f97bfb More or less done with object-tree.rst. jf3243 parents: 101 diff changeset	84 js> array.attr
29e156f97bfb More or less done with object-tree.rst. jf3243 parents: 101 diff changeset	85 gotcha
29e156f97bfb More or less done with object-tree.rst. jf3243 parents: 101 diff changeset	86
29e156f97bfb More or less done with object-tree.rst. jf3243 parents: 101 diff changeset	87 And even to functions:
5 48d5ba601286 inheritance.rst: Finished, at least for this draft. Jonathan Fine <jfine@pytex.org> parents: 3 diff changeset	88
3 65872f01ea89 inheritance.rst: Made a start on this page. Jonathan Fine <jfine@pytex.org> parents: diff changeset	89 .. code-block:: javascript
65872f01ea89 inheritance.rst: Made a start on this page. Jonathan Fine <jfine@pytex.org> parents: diff changeset	90
102 29e156f97bfb More or less done with object-tree.rst. jf3243 parents: 101 diff changeset	91 js> f = function(){}
29e156f97bfb More or less done with object-tree.rst. jf3243 parents: 101 diff changeset	92 function () {
29e156f97bfb More or less done with object-tree.rst. jf3243 parents: 101 diff changeset	93 }
29e156f97bfb More or less done with object-tree.rst. jf3243 parents: 101 diff changeset	94
29e156f97bfb More or less done with object-tree.rst. jf3243 parents: 101 diff changeset	95 js> f.attr
3 65872f01ea89 inheritance.rst: Made a start on this page. Jonathan Fine <jfine@pytex.org> parents: diff changeset	96 gotcha
65872f01ea89 inheritance.rst: Made a start on this page. Jonathan Fine <jfine@pytex.org> parents: diff changeset	97
102 29e156f97bfb More or less done with object-tree.rst. jf3243 parents: 101 diff changeset	98 .. note::
29e156f97bfb More or less done with object-tree.rst. jf3243 parents: 101 diff changeset	99
29e156f97bfb More or less done with object-tree.rst. jf3243 parents: 101 diff changeset	100 A page might have many scripts, all of which would like to modify
29e156f97bfb More or less done with object-tree.rst. jf3243 parents: 101 diff changeset	101 the Object.prototype root object. This can cause bugs and
29e156f97bfb More or less done with object-tree.rst. jf3243 parents: 101 diff changeset	102 incompatibilities. So try not to do this.
29e156f97bfb More or less done with object-tree.rst. jf3243 parents: 101 diff changeset	103
29e156f97bfb More or less done with object-tree.rst. jf3243 parents: 101 diff changeset	104
207 29c7fe19aeb5 Mark inline code using duble backticks Radomir Dopieralski <radomir.dopieralski@allegro.pl> parents: 204 diff changeset	105 However, this up-the-tree lookup does not apply if ``attr`` is found
102 29e156f97bfb More or less done with object-tree.rst. jf3243 parents: 101 diff changeset	106 earlier in the tree. We continue the previous example to show this,
29e156f97bfb More or less done with object-tree.rst. jf3243 parents: 101 diff changeset	107 and the behaviour of set.
29e156f97bfb More or less done with object-tree.rst. jf3243 parents: 101 diff changeset	108
29e156f97bfb More or less done with object-tree.rst. jf3243 parents: 101 diff changeset	109 .. code-block:: javascript
29e156f97bfb More or less done with object-tree.rst. jf3243 parents: 101 diff changeset	110
29e156f97bfb More or less done with object-tree.rst. jf3243 parents: 101 diff changeset	111 js> a.attr = 'fixed'
29e156f97bfb More or less done with object-tree.rst. jf3243 parents: 101 diff changeset	112 js> a.attr
29e156f97bfb More or less done with object-tree.rst. jf3243 parents: 101 diff changeset	113 fixed
29e156f97bfb More or less done with object-tree.rst. jf3243 parents: 101 diff changeset	114 js> root.attr
29e156f97bfb More or less done with object-tree.rst. jf3243 parents: 101 diff changeset	115 gotcha
29e156f97bfb More or less done with object-tree.rst. jf3243 parents: 101 diff changeset	116
29e156f97bfb More or less done with object-tree.rst. jf3243 parents: 101 diff changeset	117
29e156f97bfb More or less done with object-tree.rst. jf3243 parents: 101 diff changeset	118 Create
29e156f97bfb More or less done with object-tree.rst. jf3243 parents: 101 diff changeset	119 ------
3 65872f01ea89 inheritance.rst: Made a start on this page. Jonathan Fine <jfine@pytex.org> parents: diff changeset	120
5 48d5ba601286 inheritance.rst: Finished, at least for this draft. Jonathan Fine <jfine@pytex.org> parents: 3 diff changeset	121 Any tree can be constructed from its root, together with a command
207 29c7fe19aeb5 Mark inline code using duble backticks Radomir Dopieralski <radomir.dopieralski@allegro.pl> parents: 204 diff changeset	122 ``create(parent)`` that returns a new child of the given parent
5 48d5ba601286 inheritance.rst: Finished, at least for this draft. Jonathan Fine <jfine@pytex.org> parents: 3 diff changeset	123 node.
48d5ba601286 inheritance.rst: Finished, at least for this draft. Jonathan Fine <jfine@pytex.org> parents: 3 diff changeset	124
207 29c7fe19aeb5 Mark inline code using duble backticks Radomir Dopieralski <radomir.dopieralski@allegro.pl> parents: 204 diff changeset	125 In all but the most recent version of JavaScript the ``create`` function
117 d123fcf749bc Add library.js (and place create in it). jf3243 parents: 102 diff changeset	126 is not built in. However, it's easy to write one, once you know
d123fcf749bc Add library.js (and place create in it). jf3243 parents: 102 diff changeset	127 enough JavaScript. Here's how its done in the work folder's
207 29c7fe19aeb5 Mark inline code using duble backticks Radomir Dopieralski <radomir.dopieralski@allegro.pl> parents: 204 diff changeset	128 ``library.js`` file.
102 29e156f97bfb More or less done with object-tree.rst. jf3243 parents: 101 diff changeset	129
117 d123fcf749bc Add library.js (and place create in it). jf3243 parents: 102 diff changeset	130 .. literalinclude:: /core-javascript-work/library.js
d123fcf749bc Add library.js (and place create in it). jf3243 parents: 102 diff changeset	131 :language: javascript
d123fcf749bc Add library.js (and place create in it). jf3243 parents: 102 diff changeset	132 :start-after: start create
d123fcf749bc Add library.js (and place create in it). jf3243 parents: 102 diff changeset	133 :end-before: end create
102 29e156f97bfb More or less done with object-tree.rst. jf3243 parents: 101 diff changeset	134
29e156f97bfb More or less done with object-tree.rst. jf3243 parents: 101 diff changeset	135
29e156f97bfb More or less done with object-tree.rst. jf3243 parents: 101 diff changeset	136 Using create
29e156f97bfb More or less done with object-tree.rst. jf3243 parents: 101 diff changeset	137 ------------
29e156f97bfb More or less done with object-tree.rst. jf3243 parents: 101 diff changeset	138
5 48d5ba601286 inheritance.rst: Finished, at least for this draft. Jonathan Fine <jfine@pytex.org> parents: 3 diff changeset	139 Here's an example of its use:
48d5ba601286 inheritance.rst: Finished, at least for this draft. Jonathan Fine <jfine@pytex.org> parents: 3 diff changeset	140
48d5ba601286 inheritance.rst: Finished, at least for this draft. Jonathan Fine <jfine@pytex.org> parents: 3 diff changeset	141 .. code-block:: javascript
48d5ba601286 inheritance.rst: Finished, at least for this draft. Jonathan Fine <jfine@pytex.org> parents: 3 diff changeset	142
48d5ba601286 inheritance.rst: Finished, at least for this draft. Jonathan Fine <jfine@pytex.org> parents: 3 diff changeset	143 js> a = {}
48d5ba601286 inheritance.rst: Finished, at least for this draft. Jonathan Fine <jfine@pytex.org> parents: 3 diff changeset	144 js> b = create(a)
102 29e156f97bfb More or less done with object-tree.rst. jf3243 parents: 101 diff changeset	145 js> a.attr = 'apple'
5 48d5ba601286 inheritance.rst: Finished, at least for this draft. Jonathan Fine <jfine@pytex.org> parents: 3 diff changeset	146 apple
102 29e156f97bfb More or less done with object-tree.rst. jf3243 parents: 101 diff changeset	147 js> b.attr
5 48d5ba601286 inheritance.rst: Finished, at least for this draft. Jonathan Fine <jfine@pytex.org> parents: 3 diff changeset	148 apple
3 65872f01ea89 inheritance.rst: Made a start on this page. Jonathan Fine <jfine@pytex.org> parents: diff changeset	149
65872f01ea89 inheritance.rst: Made a start on this page. Jonathan Fine <jfine@pytex.org> parents: diff changeset	150
5 48d5ba601286 inheritance.rst: Finished, at least for this draft. Jonathan Fine <jfine@pytex.org> parents: 3 diff changeset	151 And a continuation of the example:
48d5ba601286 inheritance.rst: Finished, at least for this draft. Jonathan Fine <jfine@pytex.org> parents: 3 diff changeset	152
48d5ba601286 inheritance.rst: Finished, at least for this draft. Jonathan Fine <jfine@pytex.org> parents: 3 diff changeset	153 .. code-block:: javascript
48d5ba601286 inheritance.rst: Finished, at least for this draft. Jonathan Fine <jfine@pytex.org> parents: 3 diff changeset	154
48d5ba601286 inheritance.rst: Finished, at least for this draft. Jonathan Fine <jfine@pytex.org> parents: 3 diff changeset	155 js> c = create(b)
102 29e156f97bfb More or less done with object-tree.rst. jf3243 parents: 101 diff changeset	156 js> c.attr
5 48d5ba601286 inheritance.rst: Finished, at least for this draft. Jonathan Fine <jfine@pytex.org> parents: 3 diff changeset	157 apple
102 29e156f97bfb More or less done with object-tree.rst. jf3243 parents: 101 diff changeset	158 js> b.attr = 'banana'
5 48d5ba601286 inheritance.rst: Finished, at least for this draft. Jonathan Fine <jfine@pytex.org> parents: 3 diff changeset	159 banana
102 29e156f97bfb More or less done with object-tree.rst. jf3243 parents: 101 diff changeset	160 js> c.attr
5 48d5ba601286 inheritance.rst: Finished, at least for this draft. Jonathan Fine <jfine@pytex.org> parents: 3 diff changeset	161 banana
3 65872f01ea89 inheritance.rst: Made a start on this page. Jonathan Fine <jfine@pytex.org> parents: diff changeset	162
65872f01ea89 inheritance.rst: Made a start on this page. Jonathan Fine <jfine@pytex.org> parents: diff changeset	163
5 48d5ba601286 inheritance.rst: Finished, at least for this draft. Jonathan Fine <jfine@pytex.org> parents: 3 diff changeset	164 .. note::
3 65872f01ea89 inheritance.rst: Made a start on this page. Jonathan Fine <jfine@pytex.org> parents: diff changeset	165
207 29c7fe19aeb5 Mark inline code using duble backticks Radomir Dopieralski <radomir.dopieralski@allegro.pl> parents: 204 diff changeset	166 JavaScript uses an inheritance tree. By using ``create``, we can
12 4be9f1bf2fd3 Reviewed and revised existing pages, and added some new stub pages. Jonathan Fine <jfine@pytex.org> parents: 8 diff changeset	167 create any inheritance tree. All JavaScript objects are in this
4be9f1bf2fd3 Reviewed and revised existing pages, and added some new stub pages. Jonathan Fine <jfine@pytex.org> parents: 8 diff changeset	168 tree.

Mercurial > js4py

annotate core-javascript/object-tree.rst @ 213:0ea90a1819c2 default tip