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Issue 10832042: Extensions Docs Server: Doc conversion script (Closed) Base URL: svn://svn.chromium.org/chrome/trunk/src
Patch Set: everything but svn stuff Created 8 years, 4 months ago
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1 <p>
2 An <code>Event</code> is an object
3 that allows you to be notified
4 when something interesting happens.
5 Here's an example of using the
6 <code>chrome.tabs.onCreated</code> event
7 to be notified whenever there's a new tab:
8 </p>
9
10 <pre>
11 chrome.tabs.onCreated.<b>addListener(function(</b>tab<b>) {</b>
12 appendToLog('tabs.onCreated --'
13 + ' window: ' + tab.windowId
14 + ' tab: ' + tab.id
15 + ' index: ' + tab.index
16 + ' url: ' + tab.url);
17 <b>});</b>
18 </pre>
19
20 <p>
21 As the example shows,
22 you register for notification using <code>addListener()</code>.
23 The argument to <code>addListener()</code>
24 is always a function that you define to handle the event,
25 but the parameters to the function depend on
26 which event you're handling.
27 Checking the documentation for
28 <a href="tabs.html#event-onCreated"><code>chrome.tabs.onCreated</code></a>,
29 you can see that the function has a single parameter:
30 a <a href="tabs.html#type-tabs.Tab">Tab</a> object
31 that has details about the newly created tab.
32 </p>
33
34
35 <div class="doc-family extensions">
36 <h2 id="declarative">Declarative Event Handlers</h2>
37
38 <p>
39 The declarative event handlers provide a means to define rules consisting of
40 declarative conditions and actions. Conditions are evaluated in the browser
41 rather than the JavaScript engine which reduces roundtrip latencies and allows
42 for very high efficiency.
43 </p>
44
45 <p>Declarative event handlers are used for example in the <a
46 href="declarativeWebRequest.html">Declarative Web Request API</a> and possibly
47 further extension APIs in the future. This page describes the underlying
48 concepts of all declarative event handlers.
49 </p>
50
51 <h3 id="rules">Rules</h3>
52
53 <p>The simplest possible rule consists of one or more conditions and one or more
54 actions:</p>
55 <pre>
56 var rule = {
57 conditions: [ /* my conditions */ ],
58 actions: [ /* my actions */ ]
59 };
60 </pre>
61
62 <p>If any of the conditions is fulfilled, all actions are executed.</p>
63
64 <p>In addition to conditions and actions you may give each rule an identifier,
65 which simplifies unregistering previously registered rules, and a priority to
66 define precedences among rules. Priorities are only considered if rules conflict
67 each other or need to be executed in a specific order.</p>
68
69 <pre>
70 var rule = {
71 id: "my rule", // optional, will be generated if not set.
72 priority: 100, // optional, defaults to 100.
73 conditions: [ /* my conditions */ ],
74 actions: [ /* my actions */ ]
75 };
76 </pre>
77
78 <h3 id="eventobjects">Event objects</h3>
79
80 <p>
81 <a href="events.html">Event objects</a> may support rules. These event objects
82 don't call a callback function when events happer but test whether any
83 registered rule has at least one fulfilled condition and execute the actions
84 associated with this rule. Event objects supporting the declarative API have
85 three relevant methods: <a href="#method-addRules"><code>addRules()</code></a>,
86 <a href="#method-removeRules"><code>removeRules()</code></a>, and
87 <a href="#method-getRules"><code>getRules()</code></a>.
88 </p>
89
90 <h3 id="addingrules">Adding rules</h3>
91
92 <p>
93 To add rules call the <code>addRules()</code> function of the event object. It
94 takes an array of rule instances as its first parameter and a callback function
95 that is called on completion.
96 </p>
97
98 <pre>
99 var rule_list = [rule1, rule2, ...];
100 function addRules(rule_list, function callback(details) {...});
101 </pre>
102
103 <p>
104 If the rules were inserted successfully, the <code>details</code> parameter
105 contains an array of inserted rules appearing in the same order as in the passed
106 <code>rule_list</code> where the optional parameters <code>id</code> and
107 <code>priority</code> were filled with the generated values. If any rule is
108 invalid, e.g., because it contained an invalid condition or action, none of the
109 rules are added and the <a
110 href="extension.html#property-lastError">lastError</a> variable is set when
111 the callback function is called. Each rule in <code>rule_list</code> must
112 contain a unique identifier that is not currently used by another rule or an
113 empty identifier.
114 </p>
115
116 <h3 id="removingrules">Removing rules</h3>
117
118 <p>
119 To remove rules call the <code>removeRules()</code> function. It accepts an
120 optional array of rule identifiers as its first parameter and a callback
121 function as its second parameter.
122 </p>
123
124 <pre>
125 var rule_ids = ["id1", "id2", ...];
126 function removeRules(rule_ids, function callback() {...});
127 </pre>
128
129 <p>
130 If <code>rule_ids</code> is an array of identifiers, all rules having
131 identifiers listed in the array are removed. If <code>rule_ids</code> lists an
132 identifier, that is unknown, this identifier is silently ignored. If
133 <code>rule_ids</code> is <code>undefined</code>, all registered rules of this
134 extension are removed. The <code>callback()</code> function is called when the
135 rules were removed.
136 </p>
137
138 <h3 id="retrievingrules">Retrieving rules</h3>
139
140 <p>
141 To retrieve a list of currently registered rules, call the
142 <code>getRules()</code> function. It accepts an optional array of rule
143 identifiers with the same semantics as <code>removeRules</code> and a callback
144 function.
145 <p>
146
147 <pre>
148 var rule_ids = ["id1", "id2", ...];
149 function getRules(rule_ids, function callback(details) {...});
150 </pre>
151
152 <p>
153 The <code>details</code> parameter passed to the <code>calback()</code> function
154 refers to an array of rules including filled optional parameters.
155 </p>
156 </div>
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