Mozilla ESLint Plugin¶
Environments¶
These environments are available by specifying a comment at the top of the file, e.g.
/* eslint-env mozilla/chrome-worker */
There are also built-in ESLint environments available as well: http://eslint.org/docs/user-guide/configuring#specifying-environments
browser-window¶
Defines the environment for scripts that are in the main browser.xul scope ( note: includes the places-overlay environment).
places-overlay¶
Defines the environment for scripts that are in a scope where placesOverlay.xul is included.
chrome-worker¶
Defines the environment for chrome workers. This differs from normal workers by the fact that ctypes can be accessed as well.
frame-script¶
Defines the environment for frame scripts.
Rules¶
avoid-Date-timing¶
Rejects grabbing the current time via Date.now() or new Date() for timing purposes when the less problematic performance.now() can be used instead.
The performance.now() function returns milliseconds since page load. To convert that to milliseconds since the epoch, use:
performance.timing.navigationStart + performance.now()
Often timing relative to the page load is adequate and that conversion may not be necessary.
avoid-removeChild¶
Rejects using element.parentNode.removeChild(element) when element.remove() can be used instead.
balanced-listeners¶
Checks that for every occurence of ‘addEventListener’ or ‘on’ there is an occurence of ‘removeEventListener’ or ‘off’ with the same event name.
import-browser-window-globals¶
For scripts included in browser-window, this will automatically inject the browser-window global scopes into the file.
import-content-task-globals¶
For files containing ContentTask.spawn calls, this will automatically declare the frame script variables in the global scope. ContentTask is only available to test files, so by default the configs only specify it for the mochitest based configurations.
This saves setting the file as a mozilla/frame-script environment.
Note: due to the way ESLint works, it appears it is only easy to declare these variables on a file global scope, rather than function global. This may mean that they are incorrectly allowed, but given they are test files, this should be detected during testing.
import-globals¶
Checks the filename of imported files e.g. Cu.import("some/path/Blah.jsm")
adds Blah to the global scope.
Note: uses modules.json for a list of globals listed in each file.
import-globals-from¶
Parses a file for globals defined in various unique Mozilla ways.
When a “import-globals-from <path>” comment is found in a file, then all globals from the file at <path> will be imported in the current scope. This will also operate recursively.
This is useful for scripts that are loaded as <script> tag in a window and rely on each other’s globals.
If <path> is a relative path, then it must be relative to the file being checked by the rule.
import-headjs-globals¶
Import globals from head.js and from any files that were imported by head.js (as far as we can correctly resolve the path).
The following file import patterns are supported:
Services.scriptloader.loadSubScript(path)loader.loadSubScript(path)loadSubScript(path)loadHelperScript(path)import-globals-from path
If path does not exist because it is generated e.g.
testdir + "/somefile.js" we do our best to resolve it.
The following patterns are supported:
Cu.import("resource://devtools/client/shared/widgets/ViewHelpers.jsm");loader.lazyImporter(this, "name1");loader.lazyRequireGetter(this, "name2"loader.lazyServiceGetter(this, "name3"XPCOMUtils.defineLazyModuleGetter(this, "setNamedTimeout", ...)loader.lazyGetter(this, "toolboxStrings"XPCOMUtils.defineLazyGetter(this, "clipboardHelper"
mark-test-function-used¶
Simply marks test (the test method) or run_test as used when in mochitests or xpcshell tests respectively. This avoids ESLint telling us that the function is never called.
no-aArgs¶
Checks that function argument names don’t start with lowercase ‘a’ followed by a capital letter. This is to prevent the use of Hungarian notation whereby the first letter is a prefix that indicates the type or intended use of a variable.
no-cpows-in-tests¶
This rule checks if the file is a browser mochitest and, if so, checks for possible CPOW usage by checking for the following strings:
- “gBrowser.contentWindow”
- “gBrowser.contentDocument”
- “gBrowser.selectedBrowser.contentWindow”
- “browser.contentDocument”
- “window.content”
- “content”
- “content.”
Note: These are string matches so we will miss situations where the parent object is assigned to another variable e.g.:
var b = gBrowser;
b.content // Would not be detected as a CPOW.
no-single-arg-cu-import¶
Rejects calls to “Cu.import” that do not supply a second argument (meaning they add the exported properties into global scope).
no-import-into-var-and-global¶
Reject use of Cu.import (or Components.utils.import) where it attempts to
import into a var and into the global scope at the same time, e.g.
var foo = Cu.import("path.jsm", this);
This is considered bad practice as it is confusing as to what is actually being imported.
no-useless-parameters¶
Reject common XPCOM methods called with useless optional parameters (eg.
Services.io.newURI(url, null, null), or non-existent parameters (eg.
Services.obs.removeObserver(name, observer, false)).
This option can be autofixed (--fix).
no-useless-removeEventListener¶
Reject calls to removeEventListener where {once: true} could be used instead.
no-useless-run-test¶
Designed for xpcshell-tests. Rejects definitions of run_test() where the
function only contains a single call to run_next_test(). xpcshell’s head.js
already defines a utility function so there is no need for duplication.
reject-importGlobalProperties¶
Rejects calls to Cu.importGlobalProperties. Use of this function is
undesirable in some parts of the tree.
reject-some-requires¶
This takes an option, a regular expression. Invocations of
require with a string literal argument are matched against this
regexp; and if it matches, the require use is flagged.
this-top-level-scope¶
Treats top-level assignments like this.mumble = value as declaring a global.
Note: These are string matches so we will miss situations where the parent object is assigned to another variable e.g.:
var b = gBrowser;
b.content // Would not be detected as a CPOW.
use-default-preference-values¶
Require providing a second parameter to get*Pref methods instead of using a try/catch block.
use-ownerGlobal¶
Require .ownerGlobal instead of .ownerDocument.defaultView.
use-services¶
Requires the use of Services.jsm rather than Cc[].getService() where a service is already defined in Services.jsm.
var-only-at-top-level¶
Marks all var declarations that are not at the top level invalid.
Example¶
| Possible values for all rules | |
| Value | Meaning |
| 0 | Deactivated |
| 1 | Warning |
| 2 | Error |
Example configuration:
"rules": {
"mozilla/balanced-listeners": 2,
"mozilla/mark-test-function-used": 1,
"mozilla/var-only-at-top-level": 1,
"mozilla/no-cpows-in-tests": 1,
}
Tests¶
The tests for eslint-plugin-mozilla are run via mochajs on top of node. Most of the tests use the ESLint Rule Unit Test framework.
Running Tests¶
The rules have some self tests, these can be run via:
cd tools/lint/eslint/eslint-plugin-mozilla npm install npm run test
Disabling tests¶
In the unlikely event of needing to disable a test, currently the only way is by commenting-out. Please file a bug if you have to do this.
Filing Bugs¶
Bugs should be filed in the Testing product under Lint.