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Difference between revisions of "Orion/ESLint"

(Quickfix future ideas)
(new fix alls)
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| Flags trailing commas in object expressions.
| Flags trailing commas in object expressions.
|style="text-align:center;" | ✔
|style="text-align:center;" | ✔
|style="text-align:center;" | Future
|style="text-align:center;" |
!style="text-align:left;"| [ no-cond-assign]
!style="text-align:left;"| [ no-cond-assign]
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| Flags $NON-NLS$ comments that are not needed to exclude a string literal
| Flags $NON-NLS$ comments that are not needed to exclude a string literal
| style="text-align:center;" | ✔
| style="text-align:center;" | ✔
| style="text-align:center;" | Future
| style="text-align:center;" |
!style="text-align:left;"| [ new-parens]
!style="text-align:left;"| [ new-parens]

Revision as of 16:39, 6 January 2016

Orion 5.0 introduced ESLint as the validator that ships with Orion. This page captures ongoing issues.


The following sections describe all of the rules currently available in Orion and ones that we plan to add in the future.

Potential Programming Problems

These rules report about problems with your code that might have undesired or incorrect results. Warnings from these rules should be addressed.

Rule Default Severity Available Since Problem Message Details Quick Fix? Fix All?
no-comma-dangle Ignore 8.0 Trailing commas in object expressions are discouraged. Flags trailing commas in object expressions.
no-cond-assign Error 8.0 Expected a conditional expression and instead saw an assignment. Flags assignment in an if/while/do..while/for condition.
no-console Error 8.0 Discouraged use of console in browser-based code. Flags the use of console in browser-based code
no-constant-condition Error 8.0 Discouraged use of constant as a conditional expression. Flags the use of a constant as a conditional expression
no-debugger Warning 6.0 debugger' statement use is discouraged. Warns when the debugger keyword is used
no-dupe-keys Error 6.0 Duplicate object key '{key}'. Flags object literals that contain the same key more than once.
no-empty-block Warning 7.0 Empty block should be removed or commented. Flags an empty block like if (something) { }.
no-extra-semi Warning 5.0 Unnecessary semicolon. Warns when a semicolon is found where it is not needed
no-fallthrough Error 6.0 Switch case may be entered by falling through previous case. If intended, add a new comment //$FALL-THROUGH$ on the line above Flags a fallthrough case within a switch statement, unless it is explicitly commented. Future
no-regex-spaces Error 8.0 Avoid using multiple spaces in regular expressions. Use ' {${0}}' instead. Flags regular expressions that have two or more subsequent spaces. Future Future
no-reserved-keys Error 8.0 Reserved words should not be used as property keys. Checks to see if a JavaScript reserved word is being used as a property key Future
no-sparse-arrays Warning 8.0 Sparse array declarations should be avoided. Flags sparse arrays with null elements like var arr = [1, ,2] Future
no-unreachable Error 6.0 Unreachable code. Flags statements that occur after a return, throw, etc.
use-isnan Error 6.0 Use the isNaN function to compare with NaN. Warns when a comparison is done against NaN without using the isNaN function Future Future
valid-typeof Error 7.0 Invalid typeof comparison. Warns when a typeof comparison uses an invalid type.

Best Practices

These rules are not necessarily problem with your code, but are warnings that you might be doing something you probably should not be.

Rule Default Severity Available Since Problem Message Details Quick Fix? Fix All?
block-scoped-var Error - '{variable}' used outside of binding context.

Occurs when a function-scoped variable (var) is treated as if it was block scoped.

curly Ignore 6.0 Statements should be enclosed in braces. Warns when statements should be enclosed in braces, for example if(something) foo(); Future Future
eqeqeq Warning 5.0
  • Expected '===' and saw '=='.
  • Expected '!==' and saw '!='.
Warns when == or != is used
no-caller Error 9.0 arguments.{callee, caller} is deprecated. Flags references to arguments.callee and arguments.caller.
no-eval Ignore 6.0 'eval' function calls are discouraged. Warns when the eval() function is used
no-implied-eval Ignore 6.0 Implicit 'eval' function calls are discouraged. Flags calls to the string-argument form of setTimeout and setInterval, which implicitly perform eval. This rule logic was merged to be part of the no-eval rule.
no-iterator Error 8.0 Discouraged __iterator__ property use. Flags use of __iterator__ as an identifier name or property key.
no-new-array Warning 6.0 Use the array literal notation []. Flags new Array(). Future Future
no-new-func Warning 6.0 The Function constructor is eval. Flags new Function(). Future
no-new-object Warning 6.0 Use the object literal notation {}. Flags new Object(). Future
no-new-wrappers Warning 6.0 Do not use {String, Number, Boolean, Math, JSON} as a constructor. Flags new applied to any of those. Future
no-proto Error 9.0
  • Reserved name '__proto__' should not be assigned.
  • Reserved name '__proto__' should not be used as a key.
Flags use of the property __proto__ as object keys or in assignments
no-redeclare Warning 5.0 '{a}' is already defined. Usually results from having two for loops in the same function that share a loop variable declaration like var i=.... Future
no-self-compare Error - Comparing a value to itself has no effect. Flags comparisons where the left- and right-hand sides are the same.
no-shadow Warning 8.0 '{a}' is already declared in the upper scope. Flags variables that have the same name as a variable declared in an upper scope. Future
no-shadow-global Warning 9.0 '{a}' shadows a global member. Flags variables that have the same name as a variable declared in the global scope or specified environments. Future
no-throw-literal Warning 9.0 Throw an Error instead. Flags code that throws a literal, eg. throw "a problem occurred"; Future
no-undef Error 5.0 '{variable}' is not defined.
  • Flags references to a global variable that is not listed in a /*global*/ or /*globals*/ block.
  • Predefined environments (eg. node, browser, amd) can be set in a /*eslint-env*/ block.
no-unused-params Warning 6.0 Parameter '{param}' is not used. Flags parameters in function declarations / expressions if they are not being used Future
no-unused-vars Warning 5.0
  • '{a}' is not read.
  • '{a}' is read-only.
Warns when a variable is created and not used (read) or a variable that is read-only is assigned to. Future
no-use-before-define Warning 5.0 '{a}' was used before it was defined. Warns when a variable or function is used before it is defined
no-with Warning 9.0 Expected an identifier and instead saw 'with'. Treated as fatal parse error in JSLint.
radix Warning 8.0 Missing radix parameter. Warns when parseInt() called without the 2nd parameter (radix).
no-self-assign Error 11.0 Assigning to itself is pointless. Warns when a variable is being assigned to itself

Code Style

These rules are not problems in any way but will warn based on certain accepted styles for coding.

Rule Default Severity Available Since Problem Message Details Quick Fix? Fix All?
missing-doc Ignore 5.0 Missing documentation for function '{name}'. Flags missing documentation nodes on function declarations and function expressions when they appear as object properties
missing-doc-items Ignore - Missing '{a}' tag for '{b}'. Flags missing documentation for parameters, returns, throws, etc on function declarations and function expressions when they appear as object properties
missing-nls Ignore 9.0 Non-externalized string literal '{a}'. Flags String literals that are not properly NLS'd Future
unnecessary-nls Ignore 11.0 Unnecessary $NON-NLS$ tag. Flags $NON-NLS$ comments that are not needed to exclude a string literal
new-parens Error 6.0 Missing parentheses invoking constructor. Flags new Whatever Future
no-jslint Warning 7.0 The 'jslint' directive is unsupported, please use eslint-env. Flags use of the /* jslint */ directive Future
no-mixed-returns Error - Mixed return types should be avoided. Flags functions that return more than one kind of item, for example returning String and Object
no-undef-init Warning 9.0 Avoid explicitly initializing variables to 'undefined'. Warns when an explicit assignment to undefined is done, for example var foo = undefined; Future Future
semi Warning 5.0 Missing semicolon. Warns when a semicolon should be used but is not Future

Upstream ESLint Rules

Starting in Orion 11.0 we have included rule implementations from the upstream ESLint library. In the UI they are mixed in with the above categories.

Rule Default Severity Available Since Documentation Details Quick Fix? Fix All?
accessor-pairs Warning 11.0 accessor-pairs It's a common mistake in JavaScript to create an object with just a setter for a property but never have a corresponding getter defined for it. Without a getter, you cannot read the property, so it ends up not being used.
no-control-regex Error 11.0 no-control-regex Control characters are special, invisible characters in the ASCII range 0-31. These characters are rarely used in JavaScript strings so a regular expression containing these characters is most likely a mistake.
no-duplicate-case Error 11.0 no-duplicate-case A switch statements with duplicate case labels is normally an indication of a programmer error.
no-else-return Warning 11.0 no-else-return If an if block contains a return statement, the else block becomes unnecessary. Its contents can be placed outside of the block.
no-empty-character-class Error 11.0 no-empty-character-class Empty character classes in regular expressions do not match anything and can result in code that may not work as intended.
no-empty-label Error 11.0 no-empty-label Labeled statements are only used in conjunction with labeled break and continue statements. ECMAScript has no goto statement.
no-eq-null Error 11.0 no-eq-null Comparing to null without a type-checking operator (== or !=), can have unintended results as the comparison will evaluate to true when comparing to not just a null, but also an undefined value.
no-extra-boolean-cast Error 11.0 no-extra-boolean-cast In contexts such as an if statement's test where the result of the expression will already be coerced to a Boolean, casting to a Boolean via double negation (!!) is unnecessary.
no-extra-parens Warning 11.0 no-extra-parens This rule restricts the use of parentheses to only where they are necessary. It may be restricted to report only function expressions.
no-invalid-regexp Error 11.0 no-invalid-regexp This rule validates string arguments passed to the RegExp constructor.
no-negated-in-lhs Error 11.0 no-negated-in-lhs Disallow negated left operand of in operator
no-obj-calls Error 11.0 no-obj-calls ECMAScript provides several global objects that are intended to be used as-is. Some of these objects look as if they could be constructors due their capitalization (such as Math and JSON) but will throw an error if you try to execute them as functions.
no-self-compare Error 11.0 no-self-compare Comparing a variable against itself is usually an error, either an typo or refactoring error. It is confusing to the reader and may potentially introduce a runtime error.
no-irregular-whitespace Ignore 11.0 no-irregular-whitespace Invalid or irregular whitespace causes issues with ECMAScript 5 parsers and also makes code harder to debug in a similar nature to mixed tabs and spaces.

Implementing a new rule

This section explains how to implement a new linting rule. For brevity, all paths are given relative to bundles/org.eclipse.orion.client.javascript/web/ in the client repo.

First, create the tests and rule:

  1. Create a new describe("{rule-name}") block in: /js-tests/javascript/eslintRuleTests.js. Add several tests to it.
  2. Run the JS bundle tests and ensure that your new tests fail.
  3. Implement the actual logic for your rule in /eslint/lib/load-rules-async.js.
  4. Run the tests again. This time they should all pass.

To get your rule running in the Orion product's validator, there are additional steps:

  1. Create strings for the validation message(s) generated by your rule in /javascript/nls/root/problems.js.
  2. Create a short string describing what your rule does in /javascript/nls/root/messages.js.
  3. Add an entry to the orion.core.setting declaration in /javascript/plugins/javascriptPlugin.js. This allows your rule to be configured from the JS validator settings page. Make sure it references the same nameKey used in messages.js.
  4. Add a config entry for your rule to /javascript/rules.json.
  5. Add your rule to the #updated() handler in /javascript/validator.js.

Reload the JS plugin, and your rule should now be configurable from the Settings page, and properly set up for translation too.


  • Every rule needs extensive unit tests.
  • Unit tests should use Mocha.

Running the tests

  • To run the ESLint tests as part of the main JavaScript tests suite load {orion-server-url}/javascript/js-tests/JsMochaSuite.html in your web browser.
  • To run just the ESLint rule tests, load {orion-server-url}/js-tests/javascript/JsMochaSuite.html?grep=ESLint%20Rule%20Tests in your browser.
  • To run just the ESLint core tests, load {orion-server-url}/js-tests/javascript/JsMochaSuite.html?grep=ESLint%20Core%20Tests in your browser.
  • To run only a subset of the tests, add ?grep=ESLint%20Rule%20Tests onto the test page URL.

See Mocha usage options for more options.

User interface

  • Should we have a UI for configuring what rules are active? bug 424268.
  • Should we try to support .eslintrc? This would be an ideal project-scope setting.
  • Should we try to honor equivalent JSLint/JSHint flags when possible? For example /*jslint eqeqeq:false */ could disable the eqeqeq rule on a per-file basis.
    • ESLint now has its own syntax for this: /*eslint ..*/, which we are using instead.


We need to support i18n. Pre-req is bug 422278 (orion.edit.validator support for i18n).

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