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4 <title>JSCoverage user manual</title>
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12
13 <h1>JSCoverage user manual</h1>
14
15 <p>
16 JSCoverage is a tool that measures code coverage for JavaScript programs.
17 </p>
18
19 <p>
20 JSCoverage works by adding instrumentation to JavaScript code before it is
21 executed in a web browser. JSCoverage provides several alternative ways of doing
22 this:
23 </p>
24
25 <ul>
26 <li>The simplest method is to use the <code>jscoverage</code> program to generate
27 instrumented JavaScript files.
28 </li>
29 <li>Alternatively, you can use the <code>jscoverage-server</code> program, a simple web server that instruments
30 JavaScript code as it is served.
31 </li>
32 <li>Finally, <code>jscoverage-server</code> can be run with the <code>--proxy</code> option to
33 act as a proxy server which instruments any JavaScript code proxied through it.
34 </li>
35 </ul>
36
37 <p>
38 The <code>jscoverage-server</code> program (with or without the <code>--proxy</code>
39 option) has the advantage of being able to store coverage reports to the filesystem.
40 </p>
41
42 <h2>Compiling JSCoverage</h2>
43
44 <p>
45 You can compile JSCoverage on GNU/Linux or Microsoft Windows, using the GCC C++ compiler (<code>g++</code>). On
46 Windows you will require <a href="http://cygwin.com/">Cygwin</a> or <a
47 href="http://mingw.org/">MinGW/MSYS</a>.
48 </p>
49
50 <p>
51 You can extract and compile the code with the following commands:
52 </p>
53
54 <pre>
55 tar jxvf jscoverage-0.4.tar.bz2
56 cd jscoverage-0.4/
57 ./configure
58 make
59 </pre>
60
61 <p>
62 This will create the <code>jscoverage</code> and <code>jscoverage-server</code>
63 executables (<code>jscoverage.exe</code> and <code>jscoverage-server.exe</code>
64 on Windows). You can install the executables in <code>/usr/local</code> with the
65 command:
66 </p>
67
68 <pre>
69 make install
70 </pre>
71
72 <p>
73 Alternatively, you may simply copy the <code>jscoverage</code> executable and/or
74 the <code>jscoverage-server</code> executable to a suitable location in your
75 <code>PATH</code>.
76 </p>
77
78 <h2>Using the <code>jscoverage</code> program</h2>
79
80 <p>
81 To demonstrate how the <code>jscoverage</code> program works, we will use the
82 trivial example JavaScript code located in the
83 <code>doc/example/</code> directory of the JSCoverage distribution. You can run
84 this example by viewing the file <code>doc/example/index.html</code> in your web browser.
85 </p>
86
87 <p>
88 Generating code coverage statistics for this example using the
89 <code>jscoverage</code> program involves the following steps:
90 </p>
91
92 <h3>1. Instrumenting code</h3>
93
94 <p>
95 The first step is to add instrumentation to your JavaScript code. You do this by
96 executing <code>jscoverage</code> with two arguments:
97 </p>
98
99 <pre>
100 jscoverage <var>SOURCE-DIRECTORY</var> <var>DESTINATION-DIRECTORY</var>
101 </pre>
102
103 <p>
104 <var>SOURCE-DIRECTORY</var> is the directory containing the JavaScript code to be instrumented,
105 and <var>DESTINATION-DIRECTORY</var> is the name of the
106 directory to which <code>jscoverage</code> should output the instrumented code.
107 The <code>jscoverage</code> program will create <var>DESTINATION-DIRECTORY</var> if necessary and (recursively) copy
108 <var>SOURCE-DIRECTORY</var> to <var>DESTINATION-DIRECTORY</var>, instrumenting
109 any files ending with a <code>.js</code> extension.
110 </p>
111
112 <p>
113 The directory structure under <var>SOURCE-DIRECTORY</var> is preserved, so that if you have a file
114 <code><var>SOURCE-DIRECTORY</var>/dir/index.html</code> referencing the script
115 <code><var>SOURCE-DIRECTORY</var>/dir/script.js</code>, then
116 <code>jscoverage</code> will create a copy of the HTML file at
117 <code><var>DESTINATION-DIRECTORY</var>/dir/index.html</code> and an instrumented
118 version of the script at
119 <code><var>DESTINATION-DIRECTORY</var>/dir/script.js</code>.
120 In addition, <code>jscoverage</code> creates a file called <code>jscoverage.html</code>
121 which is used to execute the instrumented code.
122 </p>
123
124 <table>
125 <tr>
126 <td><pre>
127 <var>SOURCE-DIRECTORY</var>/
128 dir/
129 index.html
130 script.js
131
132 </pre></td>
133 <td class="arrow">&rarr;</td>
134 <td><pre>
135 <var>DESTINATION-DIRECTORY</var>/
136 dir/
137 index.html
138 script.js [instrumented]
139 jscoverage.html
140 </pre></td>
141 </tr>
142 </table>
143
144 <p>
145 For the example code in the <code>doc/example/</code> directory, you can execute the
146 following command line from the top-level directory of the JSCoverage distribution:
147 </p>
148
149 <pre>
150 jscoverage doc/example doc/instrumented
151 </pre>
152
153 <p>
154 This will create the directory <code>doc/instrumented/</code> and place an
155 instrumented copy of the code from <code>doc/example/</code> in
156 <code>doc/instrumented/</code>.
157 </p>
158
159 <table>
160 <tr>
161 <td><pre>
162 doc/example/
163 index.html
164 script.js
165
166 </pre></td>
167 <td class="arrow">&rarr;</td>
168 <td><pre>
169 doc/instrumented/
170 index.html
171 script.js [instrumented]
172 jscoverage.html
173 </pre></td>
174 </tr>
175 </table>
176
177 <h3>2. Executing the instrumented code in a web browser</h3>
178
179 <p>
180 Open the generated <code>jscoverage.html</code> file
181 (<code>doc/instrumented/jscoverage.html</code>) in your web browser.
182 The page contains a tabbed user interface:
183 </p>
184
185 <ul>
186 <li>The "Browser" tab is used to display pages with instrumented scripts.
187 <li>The "Summary" tab is used to display code coverage data.
188 <li>The "Source" tab is used to display JavaScript code, showing the number of times
189 each line of code was executed.
190 <li>The "About" tab displays information about the current version of JSCoverage.
191 </ul>
192
193 <p><img src="screenshot.png" alt="Screenshot"></p>
194
195 <p>
196 The "Browser" tab contains an <code>&lt;iframe&gt;</code>, which is initially empty.
197 You can load a URL into this frame by entering it into the "URL" input field and clicking the "Open in frame" button.
198 You can load any page located in <code><var>DESTINATION-DIRECTORY</var>/</code>
199 or a subdirectory underneath <code><var>DESTINATION-DIRECTORY</var>/</code>; loading a page
200 from outside <code><var>DESTINATION-DIRECTORY</var>/</code>, or from a foreign web
201 server, will give unexpected results.
202 </p>
203
204 <p>
205 For example, you can load the file <code>doc/instrumented/index.html</code> by typing
206 <code>index.html</code> in the "URL" input field (relative URLs are acceptable).
207 </p>
208
209 <p>
210 Alternatively, you can load a page into the <code>&lt;iframe&gt;</code> by
211 appending the page URL to the query string of the <code>jscoverage.html</code> URL.
212 For example, appending <code>?index.html</code> to the <code>jscoverage.html</code> URL
213 will cause the <code>index.html</code> file to be loaded automatically.
214 </p>
215
216 <p><img src="screenshot2.png" alt="Screenshot"></p>
217
218 <p>
219 For this example, the JavaScript does not execute automatically:
220 you have to select one of the radio buttons to execute the code.
221 </p>
222
223 <p><img src="screenshot3.png" alt="Screenshot"></p>
224
225 <h3>3. Generating a coverage report</h3>
226
227 <p>
228 Once the JavaScript code in the page in the "Browser" tab has been executed, click on
229 the "Summary" tab. This will display the current code coverage statistics.
230 </p>
231
232 <p><img src="screenshot4.png" alt="Screenshot"></p>
233
234 <p>
235 You can click the checkbox to show a list of statements missed during execution.
236 </p>
237
238 <p><img src="screenshot5.png" alt="Screenshot"></p>
239
240 <p>
241 You can click one of the links to get a detailed view of a JavaScript source file.
242 </p>
243
244 <p><img src="screenshot6.png" alt="Screenshot"></p>
245
246 <p>
247 As long as you do not reload the
248 <code>jscoverage.html</code> page, the coverage report statistics are
249 cumulative. If you execute more JavaScript in the frame in the "Browser" tab (e.g., by clicking on a link to
250 another scripted page, or by reloading the frame containing a scripted
251 page) and switch to the "Summary" tab again,
252 the coverage report will combine the statistics from the previous report with any newly generated statistics.
253 Reloading <code>jscoverage.html</code> resets all code coverage statistics to zero.
254 </p>
255
256 <h2>Window mode</h2>
257
258 <p>
259 In some situations it may be difficult to execute your code within the <code>&lt;iframe&gt;</code> in the
260 JSCoverage "Browser" tab. For example, the code may assume that it is running in
261 the top-level browser window, generating errors if it is executed from within a
262 frame. JSCoverage has an alternative mode of operation, called <dfn>window
263 mode</dfn>, which may be useful in this case.
264 </p>
265
266 <p>
267 To use JSCoverage in window mode, load your URL by clicking the "Open in window"
268 button instead of the "Open in frame" button. This will cause your URL to be
269 opened in a new window. (Depending on your browser settings, it may be opened in
270 a new browser tab instead.) Execute your code in this new window, and
271 then return to the <code>jscoverage.html</code> window and click the "Summary"
272 tab to get code coverage statistics.
273 </p>
274
275 <h2>Inverted mode</h2>
276
277 <p>
278 There is another alternative mode of operation, called <dfn>inverted
279 mode</dfn>. Like window mode, this allows you to avoid running your code inside an <code>&lt;iframe&gt;</code>.
280 </p>
281
282 <p>
283 Normally you load <code>jscoverage.html</code> in your web browser, and in its
284 "Browser" tab you launch your test code. In inverted mode, you do the
285 opposite: you load your test page directly in your web browser, and from there
286 you launch JSCoverage. To do this you need to add some code to your test page:
287 </p>
288
289 <pre class="sh_javascript">
290 window.open('path/to/jscoverage.html');
291 </pre>
292
293 <p>
294 The <code>"path/to/jscoverage.html"</code> should be a URL pointing to the
295 location of the <code>jscoverage.html</code> file (remember, this will be in the
296 top level of the <var>DESTINATION-DIRECTORY</var> you specified when running
297 the <code>jscoverage</code> executable).
298 </p>
299
300 <p>
301 You can place this code wherever you like in your page: for example, you could
302 attach it to a button:
303 </p>
304
305 <pre class="sh_html">
306 &lt;button type="button" onclick="window.open('path/to/jscoverage.html');"&gt;Coverage report&lt;/button&gt;
307 </pre>
308
309 <p>
310 Note that you <em>must</em> use a <code>window.open</code> call; simply making a
311 link to <code>jscoverage.html</code> is not sufficient.
312 </p>
313
314 <p>
315 An example is located in the <code>doc/example-inverted</code> directory.
316 You can instrument the code with the <code>jscoverage</code> program:
317 </p>
318
319 <pre>
320 jscoverage doc/example-inverted doc/instrumented-inverted
321 </pre>
322
323 <p>
324 You can load the page <code>doc/instrumented-inverted/index.html</code>
325 directly in your web browser.
326 From this page, you select one of the radio buttons and then click the "Coverage
327 report" button to launch the JSCoverage report.
328 </p>
329
330 <p>
331 Another example is located in the <code>doc/example-jsunit</code> directory.
332 See the <a href="faq.html#jsunit">FAQ</a> for more information.
333 </p>
334
335 <h2><code>jscoverage</code> command line options</h2>
336
337 <p>
338 The <code>jscoverage</code> program accepts the following options:
339 </p>
340
341 <dl>
342 <dt><code>-h</code>, <code>--help</code>
343 <dd>Display a brief help message.
344 <dt><code>-V</code>, <code>--version</code>
345 <dd>Display the version of the program.
346 <dt><code>-v</code>, <code>--verbose</code>
347 <dd>Explain what is being done.
348 <dt><code>--encoding=<var>ENCODING</var></code>
349 <dd>Assume that all JavaScript files use the given character encoding. The
350 default is ISO-8859-1.
351 <dt><code>--exclude=<var>PATH</var></code>
352 <dd>The command
353 <pre>
354 jscoverage --exclude=<var>PATH</var> <var>SOURCE-DIRECTORY</var> <var>DESTINATION-DIRECTORY</var>
355 </pre>
356 copies <var>SOURCE-DIRECTORY</var> to <var>DESTINATION-DIRECTORY</var>
357 recursively, but does not copy <var>SOURCE-DIRECTORY</var>/<var>PATH</var>.
358 <var>PATH</var> must be a complete path relative to <var>SOURCE-DIRECTORY</var>.
359 <var>PATH</var> can be a file or a directory (in which case the directory and
360 its entire contents are skipped). This option may be given multiple times.
361 <dt><code>--js-version=<var>VERSION</var></code>
362 <dd>Use the specified JavaScript version; valid values for <var>VERSION</var>
363 are <code>1.0</code>, <code>1.1</code>, <code>1.2</code>, ..., <code>1.8</code>,
364 or <code>ECMAv3</code> (the default).
365 <dt><code>--no-highlight</code>
366 <dd>Do not perform syntax highlighting of JavaScript code.
367 <dt><code>--no-instrument=<var>PATH</var></code>
368 <dd>The command
369 <pre>
370 jscoverage --no-instrument=<var>PATH</var> <var>SOURCE-DIRECTORY</var> <var>DESTINATION-DIRECTORY</var>
371 </pre>
372 copies <var>SOURCE-DIRECTORY</var> to <var>DESTINATION-DIRECTORY</var>
373 recursively, but does not instrument any JavaScript code in
374 <var>SOURCE-DIRECTORY</var>/<var>PATH</var>. <var>PATH</var> must be a complete
375 path relative to <var>SOURCE-DIRECTORY</var>. <var>PATH</var> can be a
376 (JavaScript) file or a directory (in which case any JavaScript files located
377 anywhere underneath the directory are not instrumented). This option may be
378 given multiple times.
379 </dl>
380
381 <h2>Query string options</h2>
382
383 <p>
384 When accessing <code>jscoverage.html</code> in a web browser, you may provide a
385 query string consisting of options separated by ampersand (<code>&amp;</code>)
386 or semicolon (<code>;</code>). Any option not containing an equals sign
387 (<code>=</code>) is considered to be a URL which will be loaded in the
388 <code>&lt;iframe&gt;</code> within the "Browser" tab.
389 </p>
390
391 <dl>
392 <dt><code>u=<var>URL</var></code>, <code>url=<var>URL</var></code>, <code>frame=<var>URL</var></code>, <code>f=<var>URL</var></code>
393 <dd>Load <var>URL</var> in the <code>&lt;iframe&gt;</code> within the "Browser" tab. (This is the same as specifying
394 an option without an equals sign.)
395 <dt><code>w=<var>URL</var></code>, <code>window=<var>URL</var></code>
396 <dd>Load <var>URL</var> in a new window (window mode).
397 <dt><code>m=<var>BOOLEAN</var></code>, <code>missing=<var>BOOLEAN</var></code>
398 <dd>Determines whether to initially display the "Missing" column in the "Summary"
399 tab. <var>BOOLEAN</var> can be
400 <code>true</code>, <code>t</code>, <code>yes</code>, <code>y</code>, <code>on</code>, <code>1</code>
401 (to display the "Missing" column), or
402 <code>false</code>, <code>f</code>, <code>no</code>, <code>n</code>, <code>off</code>, <code>0</code>
403 (to hide the "Missing" column). By default, the "Missing" column is not displayed.
404 </dl>
405
406 <h2>Using the <code>jscoverage-server</code> program</h2>
407
408 <p>
409 The <code>jscoverage-server</code> program is a simple web server. You can use
410 <code>jscoverage-server</code> to serve files from the <code>doc/example/</code>
411 directory:
412 </p>
413
414 <pre>
415 cd doc/example
416 jscoverage-server --verbose
417 </pre>
418
419 <p>
420 Once the server is running, you can access the JSCoverage web interface by
421 visiting the URL <code>http://127.0.0.1:8080/jscoverage.html</code>, and you can
422 load the <code>doc/example/index.html</code> file by entering
423 <code>index.html</code> in the "URL" input field. (Or you can do this all in
424 one step by loading the URL
425 <code>http://127.0.0.1:8080/jscoverage.html?index.html</code> in your web
426 browser.) The
427 <code>jscoverage-server</code> program automatically instruments any served
428 JavaScript code, so that code coverage data will be gathered as the code is
429 executed in your browser.
430 </p>
431
432 <p>
433 The web interface is slightly different from that generated by the
434 <code>jscoverage</code> program: it has a new tab named "Store".
435 To store coverage data, click the "Store" tab.
436 </p>
437
438 <p><img src="screenshot7.png" alt="Screenshot"></p>
439
440 <p>
441 When you click the "Store Report" button, the coverage data will be saved to a directory named <code>jscoverage-report/</code>.
442 You can view this stored report at any time by opening the file <code>jscoverage-report/jscoverage.html</code> in
443 your web browser - you don't need the <code>jscoverage-server</code> running to access it.
444 </p>
445
446 <p>
447 If you use the "Store" tab again to store coverage data, the new data will be merged with
448 the previous data in the <code>jscoverage-report/</code> directory. This can be useful,
449 for instance, if you wish to run a set of tests in different browsers and generate an
450 aggregate report which combines the data for all of them.
451 </p>
452
453 <p>
454 You can stop the server by running another instance of <code>jscoverage-server</code> with the
455 <code>--shutdown</code> option:
456 </p>
457
458 <pre>
459 jscoverage-server --shutdown
460 </pre>
461
462 <h2>Using <code>jscoverage-server --proxy</code></h2>
463
464 <p>
465 To use <code>jscoverage-server</code> as a proxy server, use the <code>--proxy</code> option:
466 </p>
467
468 <pre>
469 jscoverage-server --verbose --proxy
470 </pre>
471
472 <p>
473 Configure your browser to use an HTTP proxy with address 127.0.0.1 and port 8080.
474 You can then generate code coverage data for a web page on the server <code>example.com</code>
475 by accessing the JSCoverage web interface at the special URL <code>http://example.com/jscoverage.html</code>.
476 Note that this URL is not provided by the <code>example.com</code> server; it is automatically generated
477 by the proxy server whenever a URL with path <code>/jscoverage.html</code> is requested.
478 </p>
479
480 <p>
481 Note that if you are using Internet Explorer and running a web server on your
482 local machine, accessing the web server using a host name of
483 <code>127.0.0.1</code> or <code>localhost</code> will <em>not</em> go through
484 the proxy.
485 See the <a href="faq.html#ie-proxy">FAQ</a> for more details.
486 </p>
487
488 <h2><code>jscoverage-server</code> command line options</h2>
489
490 <dl>
491 <dt><code>-h</code>, <code>--help</code>
492 <dd>Display a brief help message.
493 <dt><code>-V</code>, <code>--version</code>
494 <dd>Display the version of the program.
495 <dt><code>-v</code>, <code>--verbose</code>
496 <dd>Explain what is being done.
497 <dt><code>--document-root=<var>PATH</var></code>
498 <dd>Serve web content from the directory given by <var>PATH</var>. The default is
499 the current directory. This option may not be given with the <code>--proxy</code> option.
500 <dt><code>--encoding=<var>ENCODING</var></code>
501 <dd>Assume that all JavaScript files use the given character encoding. The
502 default is ISO-8859-1. Note that if you use the <code>--proxy</code> option, the
503 character encoding will be determined from the <code>charset</code> parameter in
504 the <code>Content-Type</code> HTTP header.
505 <dt><code>--ip-address=<var>ADDRESS</var></code>
506 <dd>Run the server on the IP address given by <var>ADDRESS</var>. The default is <code>127.0.0.1</code>. Specify
507 <code>0.0.0.0</code> to use any address.
508 <dt><code>--js-version=<var>VERSION</var></code>
509 <dd>Use the specified JavaScript version; valid values for <var>VERSION</var>
510 are <code>1.0</code>, <code>1.1</code>, <code>1.2</code>, ..., <code>1.8</code>,
511 or <code>ECMAv3</code> (the default).
512 <dt><code>--no-highlight</code>
513 <dd>Do not perform syntax highlighting of JavaScript code.
514 <dt><code>--no-instrument=<var>URL</var></code>
515 <dd>Do not instrument JavaScript code from <var>URL</var>. If you are running <code>jscoverage-server</code>
516 with the <code>--proxy</code> option, <var>URL</var> should be a full URL. For example:
517 <pre>
518 jscoverage-server --proxy --no-instrument=http://example.com/scripts/
519 </pre>
520 Without <code>--proxy</code>, <var>URL</var> should be only the path portion of a URL:
521 <pre>
522 jscoverage-server --no-instrument=/scripts/
523 </pre>
524 This option may be given multiple times.
525 <dt><code>--port=<var>PORT</var></code>
526 <dd>Run the server on the port given by <var>PORT</var>. The default is port 8080.
527 <dt><code>--proxy</code>
528 <dd>Run as a proxy server.
529 <dt><code>--report-dir=<var>PATH</var></code>
530 <dd>Use the directory given by <var>PATH</var> for storing coverage reports. The default is
531 <code>jscoverage-report/</code> in the current directory.
532 <dt><code>--shutdown</code>
533 <dd>Stop a running instance of the server.
534 </dl>
535
536 <h2>Advanced topics</h2>
537
538 <h3>Storing coverage reports programmatically</h3>
539
540 <p>
541 If you are executing a test suite using <code>jscoverage-server</code>, you can
542 store a coverage report programmatically by having your test suite call the
543 <code>jscoverage_report</code> function (automatically generated by
544 <code>jscoverage-server</code>) after all your tests have finished running:
545 </p>
546
547 <pre class="sh_javascript">
548 if (window.jscoverage_report) {
549 jscoverage_report();
550 }
551 </pre>
552
553 <p>
554 You can specify the name of the directory in which to store the report by
555 passing the name as a parameter to the <code>jscoverage_report</code> function:
556 </p>
557
558 <pre class="sh_javascript">
559 if (window.jscoverage_report) {
560 // determine the directory name based on the browser
561 var directory;
562 if (/MSIE/.test(navigator.userAgent)) {
563 directory = 'IE';
564 }
565 else {
566 directory = 'other';
567 }
568 jscoverage_report(directory);
569 }
570 </pre>
571
572 <p>
573 This directory will be a subdirectory under the <code>jscoverage-report/</code>
574 directory (or whatever is specified with the <code>--report-dir</code> option).
575 Using the above example, the report would be stored to either
576 <code>jscoverage-report/IE/</code> or <code>jscoverage-report/other/</code>.
577 </p>
578
579 <p>
580 It is not necessary that your test suite be executed within the
581 <code>jscoverage.html</code> web interface to store a coverage report. The URL
582 of the test suite can simply be loaded directly in a web browser.
583 </p>
584
585 <p>
586 The example in <code>doc/example-jsunit/</code> demonstrates storing coverage
587 reports programmatically.
588 </p>
589
590 <h3>Ignoring certain lines of code</h3>
591
592 <p>
593 Sometimes you may wish to exclude certain lines of code from coverage
594 statistics. Some lines of code may be executed only in certain browsers; other
595 lines should never be executed at all (they may be present only to detect
596 programming errors). You can use specially formatted comments in your code to
597 tell JSCoverage to ignore certain lines of code. These lines will not be
598 included in the JSCoverage "Summary" tab; in the "Source" tab, these lines will
599 be indicated with the color yellow.
600 </p>
601
602 <p>
603 These comments take the following form:
604 </p>
605
606 <pre class="sh_javascript">
607 //#JSCOVERAGE_IF <var>CONDITION</var>
608 ...
609 //#JSCOVERAGE_ENDIF
610 </pre>
611
612 <p>
613 The comment must be formatted exactly as shown: it must be a line comment
614 starting with <code>//</code>, it must start in the first column, and it must be
615 followed by <code>#JSCOVERAGE_IF</code> or <code>#JSCOVERAGE_ENDIF</code> in
616 uppercase letters with no intervening white space.
617 </p>
618
619 <p>
620 The <var>CONDITION</var> is an ordinary JavaScript expression; if this
621 expression evaluates to <code>true</code>, then the lines of code between the
622 <code>//#JSCOVERAGE_IF</code> and <code>//#JSCOVERAGE_ENDIF</code> comments are
623 included in coverage statistics; otherwise, they are excluded from coverage
624 statistics.
625 </p>
626
627 <p>
628 For example:
629 </p>
630
631 <pre class="sh_javascript">
632 function log(s) {
633 if (window.console) {
634 //#JSCOVERAGE_IF window.console
635 console.log(s);
636 //#JSCOVERAGE_ENDIF
637 }
638 }
639 </pre>
640
641 <p>
642 You can exclude code from coverage statistics unconditionally by using
643 <code>#JSCOVERAGE_IF 0</code> or <code>#JSCOVERAGE_IF false</code>:
644 </p>
645
646 <pre class="sh_javascript">
647 function f(x) {
648 if (x === null) {
649 //#JSCOVERAGE_IF 0
650 throw 'error';
651 //#JSCOVERAGE_ENDIF
652 }
653 ...
654 </pre>
655
656 <p>
657 There is also a short form, which must appear on the line preceding an
658 <code>if</code> statement:
659 </p>
660
661 <pre class="sh_javascript">
662 //#JSCOVERAGE_IF
663 if (...) {
664 ...
665 }
666 else if (...) {
667 ...
668 }
669 ...
670 else {
671 ...
672 }
673 </pre>
674
675 <p>
676
677 In this form, there is no condition on the <code>//#JSCOVERAGE_IF</code> line
678 and no <code>//#JSCOVERAGE_ENDIF</code>. You use this form to tell JSCoverage
679 that you expect only one branch of the <code>if</code> statement to be executed;
680 coverage statistics will not be collected for the other branch(es). For
681 example:
682 </p>
683
684 <pre class="sh_javascript">
685 function log(s) {
686 //#JSCOVERAGE_IF
687 if (window.console) {
688 console.log(s);
689 }
690 else if (window.opera) {
691 opera.postError(s);
692 }
693 else {
694 throw 'no logging function available';
695 }
696 }
697 </pre>
698
699 <p>
700 Currently, <code>//#JSCOVERAGE_IF</code> comments are not recorded in stored coverage reports.
701 </p>
702
703 <h2>Caveats</h2>
704
705 <ul>
706 <li>JSCoverage adds instrumentation to JavaScript code, which will slow down execution speed.
707 Expect instrumented code to take at least twice as much time to run.
708 <li>JSCoverage currently instruments only <code>.js</code> files; it does not instrument code in <code>&lt;script&gt;</code>
709 elements in HTML files.
710 <li>HTML files must use relative URLs to reference scripts. If you use an absolute URL, your page will reference
711 the original uninstrumented script rather than the instrumented one, and no code coverage data will be collected.
712 <li>JSCoverage instruments physical lines of code rather than logical JavaScript statements; it works bests with code
713 that has exactly one statement per line. If you put multiple statements on a line, or split a line across two or more
714 statements, you may get strange results.
715 <li>JSCoverage uses frames. Some web pages that use frames may not function properly when run under JSCoverage, especially
716 those which try to access the top-level frame (<code>window.top</code>, <code>target="_top"</code>, etc.).
717 <li>JSCoverage is distributed without any warranty. See the <a href="license.html">license</a> for more details.
718 </ul>
719
720 <address>
721 Copyright &copy; 2007, 2008, 2009 <a href="http://siliconforks.com/"><img src="siliconforks-16x16.png" width="16" height="16" class="icon" alt="Silicon Forks"></a> <a href="http://siliconforks.com/">siliconforks.com</a><br>
722 <a href="mailto:jscoverage@siliconforks.com">jscoverage@siliconforks.com</a>
723 </address>
724
725 </body>
726 </html>

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