# JSCoverage user manual

JSCoverage is a tool that measures code coverage for JavaScript programs.

JSCoverage works by adding instrumentation to JavaScript code before it is executed in a web browser. JSCoverage provides several alternative ways of doing this:

- The simplest method is to use the `jscoverage` program to generate instrumented JavaScript files.
- Alternatively, you can use the `jscoverage-server` program, a simple web server that instruments JavaScript code as it is served.
- Finally, `jscoverage-server` can be run with the `--proxy` option to act as a proxy server which instruments any JavaScript code proxied through it.

The `jscoverage-server` program (with or without the `--proxy` option) has the advantage of being able to store coverage reports to the filesystem.

## Compiling JSCoverage

You can compile JSCoverage on GNU/Linux or Microsoft Windows, using the GCC C++ compiler (`g++`). On Windows you will require Cygwin or MinGW/MSYS.

You can extract and compile the code with the following commands:

    tar jxvf jscoverage-0.5.1.tar.bz2
    cd jscoverage-0.5.1/
    ./configure
    make

This will create the `jscoverage` and `jscoverage-server` executables (`jscoverage.exe` and `jscoverage-server.exe` on Windows). You can install the executables in `/usr/local` with the command:

    make install

Alternatively, you may simply copy the `jscoverage` executable and/or the `jscoverage-server` executable to a suitable location in your `PATH`.

## Using the `jscoverage` program

To demonstrate how the `jscoverage` program works, we will use the trivial example JavaScript code located in the `doc/example/` directory of the JSCoverage distribution. You can run this example by viewing the file `doc/example/index.html` in your web browser.

Generating code coverage statistics for this example using the `jscoverage` program involves the following steps:

### 1. Instrumenting code

The first step is to add instrumentation to your JavaScript code. You do this by executing `jscoverage` with two arguments:

    jscoverage SOURCE-DIRECTORY DESTINATION-DIRECTORY

SOURCE-DIRECTORY is the directory containing the JavaScript code to be instrumented, and DESTINATION-DIRECTORY is the name of the directory to which `jscoverage` should output the instrumented code. The `jscoverage` program will create DESTINATION-DIRECTORY if necessary and (recursively) copy SOURCE-DIRECTORY to DESTINATION-DIRECTORY, instrumenting any files ending with a `.js` extension.

The directory structure under SOURCE-DIRECTORY will be preserved, so that if you have a file `SOURCE-DIRECTORY/dir/index.html` referencing the script `SOURCE-DIRECTORY/dir/script.js`, then `jscoverage` will create a copy of the HTML file at `DESTINATION-DIRECTORY/dir/index.html` and an instrumented version of the script at `DESTINATION-DIRECTORY/dir/script.js`. In addition, `jscoverage` will create a file called `jscoverage.html` which will be used to execute the instrumented code.

    SOURCE-DIRECTORY/
      dir/
        index.html
        script.js
| → |
    DESTINATION-DIRECTORY/
      dir/
        index.html
        script.js [instrumented]
      jscoverage.html

For the example code in the `doc/example/` directory, you can execute the following command line from the top-level directory of the JSCoverage distribution:

    jscoverage doc/example doc/instrumented

This will create the directory `doc/instrumented/` and place an instrumented copy of the code from `doc/example/` in `doc/instrumented/`.

    doc/example/
      index.html
      script.js
| → |
    doc/instrumented/
      index.html
      script.js [instrumented]
      jscoverage.html

### 2. Executing the instrumented code in a web browser

You should generally execute your instrumented code by loading it from a web server. Using a web browser, connect to your web server and open the generated `jscoverage.html` file.

#### Warning

You should avoid accessing `jscoverage.html` using a `file:` URL. Previous versions of this manual suggested using such a URL, but recent web browsers have been adding new security restrictions on `file:` URLs, which can cause problems with JSCoverage. Use a web server to avoid these problems.

Any web server can be used. For example, you might choose to place your DESTINATION-DIRECTORY inside an Apache web server installation, so that Apache can serve files from it; or you might want to run a simpler web server, such as the `SimpleHTTPServer` that comes with Python:

    python.exe C:\Python27\Lib\SimpleHTTPServer.py

If for some reason you cannot run a web server and must use a `file:` URL, there are a few things you can try:

- If using Firefox, organize your test suite so that all your HTML files are located in the same directory, without any subdirectories.
- If using Google Chrome, try starting the browser with the `--allow-file-access-from-files` command line option.
- Try using an older web browser. IE 6 works quite well. :)

The `jscoverage.html` page contains a tabbed user interface:

- The "Browser" tab is used to display pages with instrumented scripts.
- The "Summary" tab is used to display code coverage data.
- The "Source" tab is used to display JavaScript code, showing the number of times each line of code was executed.
- The "About" tab displays information about the current version of JSCoverage.

The "Browser" tab contains an `<iframe>`, which is initially empty. You can load a URL into this frame by entering it into the "URL" input field and clicking the "Open in frame" button. You can load any page located in `DESTINATION-DIRECTORY/` or a subdirectory underneath `DESTINATION-DIRECTORY/`; loading a page from outside `DESTINATION-DIRECTORY/`, or from a foreign web server, will give unexpected results.

For example, you can load the file `doc/instrumented/index.html` by typing `index.html` in the "URL" input field (relative URLs are acceptable).

Alternatively, you can load a page into the `<iframe>` by appending the page URL to the query string of the `jscoverage.html` URL. For example, appending `?index.html` to the `jscoverage.html` URL will cause the `index.html` file to be loaded automatically.

For this example, the JavaScript does not execute automatically: you have to select one of the radio buttons to execute the code.

### 3. Generating a coverage report

Once the JavaScript code in the page in the "Browser" tab has been executed, click on the "Summary" tab. This will display the current code coverage statistics.

You can click the checkbox to show a list of statements missed during execution.

You can click one of the links to get a detailed view of a JavaScript source file.

As long as you do not reload the `jscoverage.html` page, the coverage report statistics are cumulative. If you execute more JavaScript in the frame in the "Browser" tab (e.g., by clicking on a link to another scripted page, or by reloading the frame containing a scripted page) and switch to the "Summary" tab again, the coverage report will combine the statistics from the previous report with any newly generated statistics. Reloading `jscoverage.html` resets all code coverage statistics to zero.

## Window mode

In some situations it may be difficult to execute your code within the `<iframe>` in the JSCoverage "Browser" tab. For example, the code may assume that it is running in the top-level browser window, generating errors if it is executed from within a frame. JSCoverage has an alternative mode of operation, called window mode, which may be useful in this case.

To use JSCoverage in window mode, load your URL by clicking the "Open in window" button instead of the "Open in frame" button. This will cause your URL to be opened in a new window. (Depending on your browser settings, it may be opened in a new browser tab instead.) Execute your code in this new window, and then return to the `jscoverage.html` window and click the "Summary" tab to get code coverage statistics.

## Inverted mode

There is another alternative mode of operation, called inverted mode. Like window mode, this allows you to avoid running your code inside an `<iframe>`.

Normally you load `jscoverage.html` in your web browser, and in its "Browser" tab you launch your test code. In inverted mode, you do the opposite: you load your test page directly in your web browser, and from there you launch JSCoverage. To do this you need to add some code to your test page:

    window.open('path/to/jscoverage.html');

The `"path/to/jscoverage.html"` should be a URL pointing to the location of the `jscoverage.html` file (remember, this will be in the top level of the DESTINATION-DIRECTORY you specified when running the `jscoverage` executable).

You can place this code wherever you like in your page: for example, you could attach it to a button:

    <button type="button" onclick="window.open('path/to/jscoverage.html');">Coverage report</button>

Note that you must use a `window.open` call; simply making a link to `jscoverage.html` is not sufficient.

An example is located in the `doc/example-inverted` directory. You can instrument the code with the `jscoverage` program:

    jscoverage doc/example-inverted doc/instrumented-inverted

You can load the page `doc/instrumented-inverted/index.html` directly in your web browser. From this page, you select one of the radio buttons and then click the "Coverage report" button to launch the JSCoverage report.

Another example is located in the `doc/example-jsunit` directory. See the FAQ for more information.

## `jscoverage` command line options

The `jscoverage` program accepts the following options:

`-h`, `--help`
  Display a brief help message.
`-V`, `--version`
  Display the version of the program.
`-v`, `--verbose`
  Explain what is being done.
`--encoding=ENCODING`
  Assume that all JavaScript files use the given character encoding. The default is ISO-8859-1.
`--exclude=PATH`
  The command

      jscoverage --exclude=PATH SOURCE-DIRECTORY DESTINATION-DIRECTORY

  copies SOURCE-DIRECTORY to DESTINATION-DIRECTORY recursively, but does not copy SOURCE-DIRECTORY/PATH. PATH must be a complete path relative to SOURCE-DIRECTORY. PATH can be a file or a directory (in which case the directory and its entire contents are skipped). This option may be given multiple times.
`--js-version=VERSION`
  Use the specified JavaScript version; valid values for VERSION are `1.0`, `1.1`, `1.2`, ..., `1.8`, or `ECMAv3` (the default).
`--no-highlight`
  Do not perform syntax highlighting of JavaScript code.
`--no-instrument=PATH`
  The command

      jscoverage --no-instrument=PATH SOURCE-DIRECTORY DESTINATION-DIRECTORY

  copies SOURCE-DIRECTORY to DESTINATION-DIRECTORY recursively, but does not instrument any JavaScript code in SOURCE-DIRECTORY/PATH. PATH must be a complete path relative to SOURCE-DIRECTORY. PATH can be a (JavaScript) file or a directory (in which case any JavaScript files located anywhere underneath the directory are not instrumented). This option may be given multiple times.

## Query string options

When accessing `jscoverage.html` in a web browser, you may provide a query string consisting of options separated by ampersand (`&`) or semicolon (`;`). Any option not containing an equals sign (`=`) is considered to be a URL which will be loaded in the `<iframe>` within the "Browser" tab.

`u=URL`, `url=URL`, `frame=URL`, `f=URL`
  Load URL in the `<iframe>` within the "Browser" tab. (This is the same as specifying an option without an equals sign.)
`w=URL`, `window=URL`
  Load URL in a new window (window mode).
`m=BOOLEAN`, `missing=BOOLEAN`
  Determines whether to initially display the "Missing" column in the "Summary" tab. BOOLEAN can be `true`, `t`, `yes`, `y`, `on`, `1` (to display the "Missing" column), or `false`, `f`, `no`, `n`, `off`, `0` (to hide the "Missing" column). By default, the "Missing" column is not displayed.

## Using the `jscoverage-server` program

The `jscoverage-server` program is a simple web server. You can use `jscoverage-server` to serve files from the `doc/example/` directory:

      cd doc/example
      jscoverage-server --verbose

Once the server is running, you can access the JSCoverage web interface by visiting the URL `http://127.0.0.1:8080/jscoverage.html`, and you can load the `doc/example/index.html` file by entering `index.html` in the "URL" input field. (Or you can do this all in one step by loading the URL `http://127.0.0.1:8080/jscoverage.html?index.html` in your web browser.) The `jscoverage-server` program automatically instruments any served JavaScript code, so that code coverage data will be gathered as the code is executed in your browser.

The web interface is slightly different from that generated by the `jscoverage` program: it has a new tab named "Store". To store coverage data, click the "Store" tab.

When you click the "Store Report" button, the coverage data will be saved to a directory named `jscoverage-report/`. You can view this stored report at any time by opening `jscoverage-report/jscoverage.html` in your web browser - you don't need the `jscoverage-server` running to access it.

#### Warning

The report does not work in Google Chrome when viewed using a `file:` URL. Either use a web server to serve the report (not `jscoverage-server`, but an ordinary web server) or start Google Chrome with the `--allow-file-access-from-files` command line option.

If you use the "Store" tab again to store coverage data, the new data will be merged with the previous data in the `jscoverage-report/` directory. This can be useful, for instance, if you wish to run a set of tests in different browsers and generate an aggregate report which combines the data for all of them.

You can stop the server by running another instance of `jscoverage-server` with the `--shutdown` option:

      jscoverage-server --shutdown

## Using `jscoverage-server --proxy`

To use `jscoverage-server` as a proxy server, use the `--proxy` option:

      jscoverage-server --verbose --proxy

Configure your browser to use an HTTP proxy with address 127.0.0.1 and port 8080. You can then generate code coverage data for a web page on the server `example.com` by accessing the JSCoverage web interface at the special URL `http://example.com/jscoverage.html`. Note that this URL is not provided by the `example.com` server; it is automatically generated by the proxy server whenever a URL with path `/jscoverage.html` is requested.

Note that if you are using Internet Explorer and running a web server on your local machine, accessing the web server using a host name of `127.0.0.1` or `localhost` will not go through the proxy. See the FAQ for more details.

## `jscoverage-server` command line options

`-h`, `--help`
  Display a brief help message.
`-V`, `--version`
  Display the version of the program.
`-v`, `--verbose`
  Explain what is being done.
`--document-root=PATH`
  Serve web content from the directory given by PATH. The default is the current directory. This option may not be given with the `--proxy` option.
`--encoding=ENCODING`
  Assume that all JavaScript files use the given character encoding. The default is ISO-8859-1. Note that if you use the `--proxy` option, the character encoding will be determined from the `charset` parameter in the `Content-Type` HTTP header.
`--ip-address=ADDRESS`
  Run the server on the IP address given by ADDRESS. The default is `127.0.0.1`. Specify `0.0.0.0` to use any address.
`--js-version=VERSION`
  Use the specified JavaScript version; valid values for VERSION are `1.0`, `1.1`, `1.2`, ..., `1.8`, or `ECMAv3` (the default).
`--mozilla`
  Specify that the source directory contains an application based on the Mozilla platform (see below).
`--no-highlight`
  Do not perform syntax highlighting of JavaScript code.
`--no-instrument=URL`
  Do not instrument JavaScript code from URL. If you are running `jscoverage-server` with the `--proxy` option, URL should be a full URL. For example:

      jscoverage-server --proxy --no-instrument=http://example.com/scripts/

  Without `--proxy`, URL should be only the path portion of a URL:

      jscoverage-server --no-instrument=/scripts/

  This option may be given multiple times.
`--port=PORT`
  Run the server on the port given by PORT. The default is port 8080.
`--proxy`
  Run as a proxy server.
`--report-dir=PATH`
  Use the directory given by PATH for storing coverage reports. The default is `jscoverage-report/` in the current directory.
`--shutdown`
  Stop a running instance of the server.

## Advanced topics

### Storing coverage reports programmatically

If you are executing a test suite using `jscoverage-server`, you can store a coverage report programmatically by having your test suite call the `jscoverage_report` function (automatically generated by `jscoverage-server`) after all your tests have finished running:

    if (window.jscoverage_report) {
      jscoverage_report();
    }

You can specify the name of the directory in which to store the report by passing the name as a parameter to the `jscoverage_report` function:

    if (window.jscoverage_report) {
      // determine the directory name based on the browser
      var directory;
      if (/MSIE/.test(navigator.userAgent)) {
        directory = 'IE';
      }
      else {
        directory = 'other';
      }
      jscoverage_report(directory);
    }

This directory will be a subdirectory under the `jscoverage-report/` directory (or whatever is specified with the `--report-dir` option). Using the above example, the report would be stored to either `jscoverage-report/IE/` or `jscoverage-report/other/`.

It is not necessary that your test suite be executed within the `jscoverage.html` web interface to store a coverage report. The URL of the test suite can simply be loaded directly in a web browser.

The example in `doc/example-jsunit/` demonstrates storing coverage reports programmatically.

### Ignoring certain lines of code

Sometimes you may wish to exclude certain lines of code from coverage statistics. Some lines of code may be executed only in certain browsers; other lines should never be executed at all (they may be present only to detect programming errors). You can use specially formatted comments in your code to tell JSCoverage to ignore certain lines of code. These lines will not be included in the JSCoverage "Summary" tab; in the "Source" tab, these lines will be indicated with the color yellow.

These comments take the following form:

    //#JSCOVERAGE_IF CONDITION
    ...
    //#JSCOVERAGE_ENDIF

The comment must be formatted exactly as shown: it must be a line comment starting with `//`, it must start in the first column, and it must be followed by `#JSCOVERAGE_IF` or `#JSCOVERAGE_ENDIF` in uppercase letters with no intervening white space.

The CONDITION is an ordinary JavaScript expression; if this expression evaluates to `true`, then the lines of code between the `//#JSCOVERAGE_IF` and `//#JSCOVERAGE_ENDIF` comments are included in coverage statistics; otherwise, they are excluded from coverage statistics.

For example:

    function log(s) {
      if (window.console) {
    //#JSCOVERAGE_IF window.console
        console.log(s);
    //#JSCOVERAGE_ENDIF
      }
    }

You can exclude code from coverage statistics unconditionally by using `#JSCOVERAGE_IF 0` or `#JSCOVERAGE_IF false`:

    function f(x) {
      if (x === null) {
    //#JSCOVERAGE_IF 0
        throw 'error';
    //#JSCOVERAGE_ENDIF
      }
      ...

There is also a short form, which must appear on the line preceding an `if` statement:

    //#JSCOVERAGE_IF
    if (...) {
      ...
    }
    else if (...) {
      ...
    }
    ...
    else {
      ...
    }

In this form, there is no condition on the `//#JSCOVERAGE_IF` line and no `//#JSCOVERAGE_ENDIF`. You use this form to tell JSCoverage that you expect only one branch of the `if` statement to be executed; coverage statistics will not be collected for the other branch(es). For example:

    function log(s) {
    //#JSCOVERAGE_IF
      if (window.console) {
        console.log(s);
      }
      else if (window.opera) {
        opera.postError(s);
      }
      else {
        throw 'no logging function available';
      }
    }

Currently, `//#JSCOVERAGE_IF` comments are not recorded in stored coverage reports.

### Code coverage for Mozilla platform applications

JSCoverage can be used to generate code coverage data for applications based on the Mozilla platform.

#### Warning

The functionality described here is highly experimental. It may change in future versions.

A simple example program is included in the `doc/example-mozilla/` directory. You can instrument and run this program as follows:

    jscoverage --mozilla --no-instrument=defaults doc/example-mozilla doc/example-mozilla-instrumented
    xulrunner doc/example-mozilla-instrumented/application.ini -console

Note that the `--mozilla` option is used to specify that the program is based on the Mozilla platform. Also, the code in the `defaults/` directory is skipped because the `.js` files in this directory are preferences files (and are different from ordinary JavaScript files). XULRunner is used to run the instrumented application:

The JavaScript code in the application is executed by selecting a radio button:

When the application is exited, a coverage report is stored in a subdirectory of the application's directory named `jscoverage-report/`. You can view the report in a web browser by opening the `jscoverage.html` file in this directory (i.e., `doc/example-mozilla-instrumented/jscoverage-report/jscoverage.html`).

## Caveats

- JSCoverage adds instrumentation to JavaScript code, which will slow down execution speed. Expect instrumented code to take at least twice as much time to run.
- JSCoverage currently instruments only `.js` files; it does not instrument code in `<script>` elements in HTML files.
- HTML files must use relative URLs to reference scripts. If you use an absolute URL, your page will reference the original uninstrumented script rather than the instrumented one, and no code coverage data will be collected.
- JSCoverage instruments physical lines of code rather than logical JavaScript statements; it works bests with code that has exactly one statement per line. If you put multiple statements on a line, or split a line across two or more statements, you may get strange results.
- JSCoverage uses frames. Some web pages that use frames may not function properly when run under JSCoverage, especially those which try to access the top-level frame (`window.top`, `target="_top"`, etc.).
- JSCoverage is distributed without any warranty. See the license for more details.