Warnings

How to tell closure compiler which warnings you want

Introduction

Closure Compiler has a --warning_level flag that gives you a few high-level options to control what warnings you see. The --warning_level flag gives you an easy way to choose the most common options. But even --warning_level=VERBOSE doesn't give you all the warnings that Closure Compiler can emit, and sometimes you want more fine-grained control.

Warnings Level API

Closure Compiler has an API for configuring the errors and warnings that you would like to see, and what level they're emitted at.

Flag API	Java API	Effect
--jscomp_error=<group>	options.setWarningLevel("<group>", CheckLevel.ERROR);	Makes all warnings of the given group to build-breaking error.
--jscomp_warning=<group>	options.setWarningLevel("<group>", CheckLevel.WARNING);	Makes all warnings of the given group a non-breaking warning.
--jscomp_off=<group>	options.setWarningLevel("<group>", CheckLevel.OFF);	Silences all warnings of the given group.

Warnings Categories

In the examples above, <group> is a pre-defined category of warnings.

Run the compiler with the --help flag to get a comprehensive up-to-date list.

The following table describes the available diagnostic groups.

Name	Effect	Default Value
accessControls	Warnings when @deprecated, @private, @protected, or @package are violated.	OFF
ambiguousFunctionDecl	Warnings about ambiguous definitions of functions. On Chrome, if (false) { function f() {} } declared 'f' in the global scope anyway. Future versions of javascript forbid this, because the actual semantics differ between browsers.	ERROR
checkDebuggerStatement	Warnings when the 'debugger' keyword is used.	OFF
checkEventfulObjectDisposal	Warnings about undisposed eventful objects.	OFF
checkRegExp	Warnings about weird regular expression literals	OFF
checkTypes	Type-checking	WARNING
checkVars	Warnings when vars are not declared or declared multiple times in the global scope.	ERROR
closureDepMethodUsageChecks	Warnings about misused goog.provide/goog.require calls	ERROR
conformanceViolations	Warnings about conformance violations and possible conformance violations.	WARNING
constantProperty	Warnings when a member property marked @const is reassigned.	OFF
const	Warnings when a variable or member property marked @const is reassigned.	OFF
deprecatedAnnotations	Warnings when using annotations that are deprecated	OFF
deprecated	Warnings when non-deprecated code accesses code that's marked @deprecated	OFF
duplicateMessage	Warnings when two i18n messages have the same id	ERROR
duplicate	Warnings when a variable is declared twice in the global scope	ERROR
es3	Warnings about EcmaScript3	ERROR
es5Strict	Warnings about EcmaScript5 strict mode	ERROR
externsValidation	Warnings about malformed externs files	WARNING
extraRequire	Warnings about unnecessary goog.require calls	OFF
fileoverviewTags	Warnings about duplicate @fileoverview tags	WARNING
globalThis	Warnings about improper use of the global this.	WARNING
inferredConstCheck	Warnings if a @const declaration contains no declared type and the compiler cannot infer one	OFF
internetExplorerChecks	Warnings about syntax error on Internet Explorer.	ERROR
invalidCasts	Warnings about invalid type casts.	WARNING
misplacedTypeAnnotation	Warnings about jsdoc type annotations that are misplaced	WARNING
missingGetCssName	Warnings about strings that should only be used inside calls to goog.getCssName	OFF
missingProperties	Warnings about whether a property will ever be defined on an object. Part of type-checking.	OFF
missingProvide	Warnings if missing a goog.provide('Foo') when defining a Foo class	OFF
missingRequire	Warnings if missing a goog.require('Foo') when a new Foo() is encountered	OFF
missingReturn	Warnings if missing return in a function which a non-void return type	OFF
newCheckTypes	Warnings from new type checker	OFF
nonStandardJsDocs	Warnings when JSDoc has annotations that the compiler thinks you misspelled.	WARNING
reportUnknownTypes	Warnings for any place in the code where type is inferred to ?. NOT RECOMMENDED!	OFF
strictModuleDepCheck	Warnings about all references potentially violating module dependencies	OFF
suspiciousCode	Warning about things like missing semicolons and comparisons to NaN	WARNING
tweakValidation	Warnings about goog.tweak primitives	OFF
typeInvalidation	Warn about properties that cannot be disambiguated when using type based optimizations	OFF
undefinedNames	Warnings when a property of a global name is not defined.	OFF
undefinedVars	Warnings when a variable is never defined.	ERROR
unknownDefines	Warnings when unknown @define values are specified.	WARNING
useOfGoogBase	Warnings aout usages of goog.base, which is not compatible with strict mode	OFF
uselessCode	Warnings when the compiler sees useless code that it plans to remove.	WARNING
violatedModuleDep	Warnings when there are references in earlier modules to variables defined in later modules	ERROR
visibility	Warnings when @private and @protected are violated.	OFF

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Defining Your Own Categories

If there is a category of warnings that you would like to configure but is not listed in the table above, it is easy to define a new one.

1. Find the unique identifier of the warnings that you'd like to configure.
2. Create a new DiagnosticGroup that gives this warning category a human-readable name, and add it to our central repository of warnings categories: https://github.com/google/closure-compiler/blob/master/src/com/google/javascript/jscomp/DiagnosticGroups.java
3. Send us a patch!

This is how we "canary" new warnings until we feel they're stable.

@suppress Tags

You can also silence warnings by adding JSDoc annotations to your code. All of the warnings categories above can be used in a @suppress tag in a @fileoverview JSDoc comment or a function JSDoc comment. For example,

/**
 * @fileoverview This is a file where deprecation checks are disabled.
 * @suppress {deprecated}
 */

/**
 * This is a function where type checking is disabled.
 * @suppress {checkTypes}
 */
function f() { /** ... */ }

There is also one warning category that you can suppress with @suppress tags, but is not available from the command-line.

/** @suppress {duplicate} */ foo.prop = ...

Suppresses warnings about a declaration of the same method or property twice in the global scope.

If you want to suppress many warnings at once, you can write

/** @suppress {duplicate, accessControls} */ function f() { ... }

or

/** @suppress {duplicate|accessControls} */ function f() { ... }