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=`	`options.setWarningLevel(, CheckLevel.ERROR);`	Makes all warnings of the given type to build-breaking error.
`--jscomp_warning=`	`options.setWarningLevel(, CheckLevel.WARNING);`	Makes all warnings of the given type a non-breaking warning.
`--jscomp_off=`	`options.setWarningLevel(, CheckLevel.OFF);`	Silences all warnings of the given type.

Warnings Categories

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

**Flag API**	**Java API**	**Effect**	**Default Value**
accessControls	`DiagnosticGroups.ACCESS_CONTROLS`	Warnings when @deprecated, @private, or @protected are violated.	OFF
ambiguousFunctionDecl	`DiagnosticGroups.AMBIGUOUS_FUNCTION_DECL`	Warnings about ambiguous definitions of functions	WARNING
checkDebuggerStatement	`DiagnosticGroups.DEBUGGER_STATEMENT_PRESENT`	Check for the use of the `debugger` statement	OFF
checkRegExp	`DiagnosticGroups.CHECK_REGEXP`	Check for regular expression literal problems	OFF
checkTypes	`DiagnosticGroups.CHECK_TYPES`	Type-checking	OFF by default, WARNING on `--warning_level=VERBOSE`
checkVars	`DiagnosticGroups.CHECK_VARS`	Warnings when vars are not declared.	OFF by default, ERROR on `--warning_level=VERBOSE`
const	`DiagnosticGroups.CONST`	Warnings when @const annotated properties or variables are reassigned or deleted.	OFF
constantProperty	`DiagnosticGroups.CONSTANT_PROPERTY`	Warnings when @const annotated properties are reassigned or deleted.	OFF
deprecated	`DiagnosticGroups.DEPRECATED`	Warnings when non-deprecated code accesses code that's marked @deprecated	OFF by default, WARNING on `--warning_level=VERBOSE`
duplicate	`DiagnosticGroups.DUPLICATE`	Warnings when a variable is declared twice in the global scope	OFF by default, ERROR on `--warning_level=VERBOSE`
es5Strict	`DiagnosticGroups.ES5_STRICT`	Warnings about code that is invalid in EcmaScript 5 Strict mode	WARNING
externsValidation	`DiagnosticGroups.EXTERNS_VALIDATION`	Warnings about malformed externs files	WARNING
fileoverviewTags	`DiagnosticGroups.FILEOVERVIEW_JSDOC`	Warnings about duplicate @fileoverview tags	WARNING
globalThis	`DiagnosticGroups.GLOBAL_THIS`	Warnings about [improper use of the global this](http://closuretools.blogspot.com/2010/10/this-this-is-your-this.html).	OFF by default, WARNING on `--warning_level=VERBOSE`
internetExplorerChecks	`DiagnosticGroups.INTERNET_EXPLORER_CHECKS`	Warnings about syntax errors on Internet Explorer, like trailing commas.	ERROR
invalidCasts	`DiagnosticGroups.INVALID_CASTS`	Warnings about invalid type casts.	OFF by default, WARNING when type checking is on
missingProperties	`DiagnosticGroups.MISSING_PROPERTIES`	Warnings about whether a property will ever be defined on an object. Part of type-checking.	OFF by default, WARNING on `--warning_level=VERBOSE`
nonStandardJsDocs	`DiagnosticGroups.NON_STANDARD_JS_DOCS`	Warnings when JSDoc has annotations that the compiler thinks you misspelled.	WARNING
strictModuleDepCheck	`DiagnosticGroups.STRICT_MODULE_DEP_CHECK `	Warnings about all references potentially violating module dependencies	OFF
suspiciousCode	`DiagnosticGroups.SUSPICIOUS_CODE`	Warning about things like missing missing semicolons and comparisons to NaN	WARNING
undefinedNames	`DiagnosticGroups.UNDEFINED_NAMES`	Warnings when properties of global names are undefined.	OFF by default, WARNING on `--warning_level=VERBOSE`
undefinedVars	`DiagnosticGroups.UNDEFINED_VARS`	Warnings when variables are undefined.	OFF by default, ERROR on `--warning_level=VERBOSE`
unknownDefines	`DiagnosticGroups.UNKNOWN_DEFINES`	Warnings when unknown @define values are specified.	WARNING
uselessCode	`DiagnosticGroups.USELESS_CODE`	Warnings when the compiler sees useless code that it plans to remove.	WARNING
visibility	`DiagnosticGroups.VISIBILITY`	Warnings when @private and @protected are violated.	OFF

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: http://code.google.com/p/closure-compiler/source/browse/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.