Closure Compiler Service API Reference

Overview

To request compiled code or other information from the Closure Compiler service, you must send an HTTP POST request to the URL https://closure-compiler.appspot.com/compile. The body of the request must contain the parameters listed in Required Request Parameters, and it can also contain any of the optional parameters listed in Optional Request Parameters.

If the server fails to process your request, you will receive a server error message. These messages are described in the Error Messages section.

Request Parameters

Required Request Parameters

js_code or code_url

The JavaScript to be compiled. You must include at least one of these parameters, and you can include both.

The js_code parameter must be a string containing JavaScript, such as alert('hello').

The code_url parameter must contain the URL of a JavaScript file. You can include multiple code_url parameters to specify multiple input files.

compilation_level

The degree of compression and optimization to apply to your JavaScript. There are three possible compilation levels:

WHITESPACE_ONLY: Just removes whitespace and comments from your JavaScript.
SIMPLE_OPTIMIZATIONS: Performs compression and optimization that does not interfere with the interaction between the compiled JavaScript and other JavaScript. This level renames only local variables. See Communicating with the API for more information about compiling with SIMPLE_OPTIMIZATIONS.
ADVANCED_OPTIMIZATIONS: Achieves the highest level of compression by renaming symbols in your JavaScript. When using ADVANCED_OPTIMIZATIONS compilation you must perform extra steps to preserve references to external symbols. See Advanced Compilation and Externs for more information about ADVANCED_OPTIMIZATIONS.

The compilation_level parameter defaults to a value of SIMPLE_OPTIMIZATIONS.

output_format

The format for the Closure Compiler service's output. There are three possible output formats:

xml

The xml output format wraps the requested information in valid XML.

The XML output looks like this:

        <compilationResult>
          <compiledCode>var a="hello";alert(a);</compiledCode>
          <statistics>
            <originalSize>98</originalSize>
            <compressedSize>35</compressedSize>
            <compileTime>0</compileTime>
          </statistics>
        </compilationResult>

The compiledCode section contains the compressed JavaScript that the Closure Compiler service produced. This section only appears if you include an output_info parameter with a value of compiled_code in the request. Similarly, the statistics section only appears if you include an output_info parameter with a value of statistics.

If you include an output_info parameter with a value of warnings and the compiler produces a warning, the output will include a warnings tag:

        <compilationResult>
         ...
         <warnings>
           <warning type="JSC_NO_SIDE_EFFECT" file="default.js" lineno="12" charno="3"  line="delete 1;">warning 1</warning>
           <warning type="JSC_UNUSED_VAR" file="default.js" lineno="13" charno="13" line="delete 1;">warning 2 </warning>
         </warnings>
          ...
        </compilationResult>

If you include an output_info with a value of errors, the Closure Compiler service will include an errors tag if your code contains a syntax error or other problem that prevents compilation. The errors tag looks like this:

        <compilationResult>
          ...
          <errors>
            <error type="JSC_NO_SIDE_EFFECT" file="default.js" lineno="12" charno="3"  line="var x=-'hello';">error 1 </error>
            <error type="JSC_UNUSED_VAR" file="default.js" lineno="13" charno="13" line="var x=-'hello'">error 2 </error>
          </errors>
          ...
        </compilationResult>

The file, line, and col attributes of the error and warning tags indicate where the Closure Compiler service encountered the error.

If the Closure Compiler service encounters an error that prevents the processing of your input, the output looks like this:

        <compilationResult>
          <serverErrors>
            <error code="1">Over quota</error>
          </serverErrors>
        </compilationResult>

json

The json output format wraps the requested information in a JavaScript Object Notation (JSON) string. Evaluation of this string as JavaScript returns a JavaScript Object.

The JSON output looks like this:

{
"compiledCode":/* raw code here */,
{"errors": [
  {"charno":4321,
   "error":"ERROR: You failed.",
   "lineno":1234,
   "file":"default.js",
   "type":"ERROR_TYPE",
   "line":"var x=-'hello';"}],
"warnings": [
  {"charno":4321,
   "lineno":1234,  
   "file":"default.js",
   "type":"ERROR_TYPE",
   "warning":"Warning: You did something wrong!",
   "line":"delete 1;"}]
"serverErrors":[
  {"code":123,"error":"Over quota"}
  ],
"statistics":{
  "originalSize":10,
  "compressedSize":3000
  "compileTime":10
  }
}

The JSON format is similar to the XML format: every tag in the XML output corresponds to a property of the same name in the JSON object

text

The text output format returns raw text without tags or JSON brackets. If the output_info includes compiled_code, the text contains JavaScript. If the output_info includes warnings, the text contains warning messages. If the output_info includes statistics, the text contains statistics.

The output_format parameter defaults to a value of text.

output_info

Indicates the kind of output you want from the compiler. There are four possible kinds of output:

compiled_code

A compressed and optimized version of your input JavaScript.

warnings

Messages that indicate possible bugs in your JavaScript.

errors

Messages that indicate syntax errors or other errors in your JavaScript.

statistics

Information about the degree of compression that the Closure Compiler achieves. For xml output, the Closure Compiler service returns statistics in the following format:

        <compilationResult>
          ...
          <statistics>
            <firstStatisticName>24</firstStatisticName>
            <secondStatisticName>15</secondStatisticName>
          </statistics>
        </compilationResult>

Optional Request Parameters

js_externs

The value of this parameter must be JavaScript code that declares function names or other symbols. Use js_externs to preserve symbols that are defined outside of the code you are compiling. The js_externs parameter only has an effect if you are using a compilation_level of ADVANCED_OPTIMIZATIONS. See Advanced Compilation for more information.

externs_url

The value of this parameter must be the URL of a file containing JavaScript that declares function names or other symbols. The symbols declared in this file are preserved in exactly the same way as symbols listed directly in the js_externs parameter. The externs_url parameter only has an effect if you are using a compilation_level of ADVANCED_OPTIMIZATIONS. See Advanced Compilation for more information.

You can specify this parameter multiple times if you have multiple externs files.

exclude_default_externs

By default, the Closure Compiler service uses a standard externs file that declares common externally defined symbols like document and all its methods. If you do NOT want to use these common externs, include in your request an exclude_default_externs parameter with a value of true.

See Advanced Compilation and Externs for more information about externs.

output_file_name

If present, the Closure Compiler service caches the compiled code for one hour and makes it available through a special URL. During this hour you can test the compiled code by pointing your browser to this URL. The URL has this form:

https://closure-compiler.appspot.com/code/bf067f356d510e1c7b81347eb84f65d2/[value of output_file_name]

formatting

If present, this parameter must have a value of pretty_print or print_input_delimiter. You can provide multiple formatting parameters in the same request. The pretty_print and print_input_delimiter values affect different aspects of the formatting, so you can include both without affecting the way either works.

pretty_print

If the request contains a formatting parameter with a value of pretty_print, the Closure Compiler service adds line breaks and indentation to its output code to make the code easier for humans to read. For example, output with pretty_print turned on looks like this:

function hello(a) {
  alert("Hello, " + a)
}
hello("New user");

Output with pretty_print turned off looks like this:

function hello(a){alert("Hello, "+a)}hello("New user");

print_input_delimiter

If the request contains a formatting parameter with a value of print_input_delimiter, the Closure Compiler service adds a separator between the compiler outputs for each file you compile. For example, if you compile two files together, the output looks like this:

// Input 0
alert("hi");
// Input 1
alert("bye");

The compiler inserts the // Input X delimiters to mark the boundaries between files. Note that the delimiters are comments, so they do not interfere with the execution of the JavaScript.

Each JavaScript file you provide with a code_url parameter has a corresponding delimited section in the compiler output. The Closure Compiler service treats all input from js_code parameters as if it comes from a single file.

Input delimiters have many potential uses, including helping you to figure out which inputs are contributing the most to the size of the compiled code.

use_closure_library

If you give the use_closure_library parameter a value of true, the compiler looks for goog.require() statements in the source code and supplies the Closure Library code requested by any such statements. It also performs optimizations designed specifically for Closure Library code. See the Closure Library documentation for more information about the Closure Library. See Finding Your Way around the Closure Library for more information about the goog.require() function.

The use_closure_library parameter defaults to false.

warning_level

Indicates the amount of information you want from the compiler about possible problems in your code. The warning_level parameter only has an effect when an output_info parameter with a value of warnings is also supplied. There are three possible warning levels:

QUIET: Outputs only syntax error messages and warnings generated by the optimization passes included in the compilation_level for the current compiler run.
DEFAULT: In addition to syntax errors and warnings generated by optimization passes, outputs warnings generated by selected code-checking passes.
VERBOSE: In addition to syntax errors and warnings generated by optimization passes, outputs warnings generated by all code-checking passes.

The warning_level parameter defaults to a value of DEFAULT.

language

The language parameter refers to which version of ECMAScript to assume when checking for errors in your code.

ECMASCRIPT3: Checks code assuming ECMAScript 3 compliance, and gives errors for code using features only present in later versions of ECMAScript.
ECMASCRIPT5: Checks code assuming ECMAScript 5 compliance, allowing new features not present in ECMAScript 3, and gives errors for code using features only present in later versions of ECMAScript.
ECMASCRIPT5_STRICT: Like ECMASCRIPT5 but assumes compliance with strict mode ("use strict";).
ECMASCRIPT6: Checks code assuming ECMAScript 6 compliance, allowing new features not present in ECMAScript 5.
ECMASCRIPT6_STRICT: Like ECMASCRIPT6 but assumes compliance with strict mode ("use strict";).

The language parameter defaults to a value of ECMASCRIPT6.

language_out

The language_out parameter refers to which version of ECMAScript your code will be returned in. It accepts the same options as language and is used to transpile between different levels of ECMAScript.

The default value is ECMASCRIPT5.

use_types_for_optimization

The use_types_for_optimization parameter controls whether the compiler will use type information to optimize your code. Incorrect type information may cause the compiler to make invalid assumptions about your code and do invalid optimizations.

The use_types_for_optimization parameter is false by default.

Error Messages

If the server fails to process your request, you will receive one of the server error messages listed in the table below. Note that these server error messages are different from compiler errors and warnings. Compiler errors and warnings indicate that Closure Compiler found a problem in your JavaScript code. Server error messages indicate that the compiler is not able to process your code at all because of an error in your request.

Error Code	Error Message	Meaning
`2`	Unknown output mode.	The value of the `output_format` parameter is something other than `xml`, `json`, or `text`.
`4`	Unknown compression level.	The value of the `compilation_level` parameter is something other than `WHITESPACE_ONLY`, `SIMPLE_OPTIMIZATIONS`, or `ADVANCED_OPTIMIZATIONS`.
`8`	POST data too large.	The size of the data you sent to the Closure Compiler service exceeds 200,000 bytes. Both the Compiler Service UI and your API calls use an HTTP POST request to communicate with the service, and the total amount of data sent in this request cannot exceed 200,000 bytes. For API calls, this limit applies to the total amount of text in all request parameters. For the Closure Compiler UI, this limit applies to the total amount of text in both the source code and the compiler options like `@code_url`. If your request is too big, either move source code into separate files and reference them using `@code_url`, or use the Closure Compiler application on your local machine.
`9`	File too large.	The total amount of code from all `code_url` files, all `externs_url` files, all `js_code` code and all `js_externs` code exceeds 1024000 bytes.
`10`	Cannot retrieve content from URL.	An error occurred when the Closure Compiler service tried to retrieve either a JavaScript file indicated in the `code_url` parameter or an externs file indicated in the `externs_url` parameter. Check that the URL is correct and that the permissions of the file allow it to be viewed.
`12`	URL is not formed properly.	The value of either the `code_url` parameter or the `externs_url` parameter is not a well-formed URL.
`13`	No output information to produce, yet compilation was requested.	No `output_info` parameter has been specified.
`14`	Unknown output_info value	The value of an `output_info` parameter is something other than `compiled_code`, `warnings`, or `statistics`.
`16`	Unknown warning level	The value of the `warning_level` parameter is something other than `QUIET`, `DEFAULT`, or `VERBOSE`.
`17`	Unknown formatting option.	The value of the `formatting` parameter is something other than `pretty_print`.
`18`	Unknown parameter in HTTP request	The HTTP request contains a parameter other than one of the ones listed in this document.
`19`	Illegal value for output_file_name	The output file name contains a character a number, letter, dot, underscore, or dash, or it contains two consecutive dots (`..`)
`22`	Too many compiles performed recently. Try again later.	You have submitted too many compiles from your machine. After an hour, you should be able to perform compiles again.
`23`	Compiler exception (with backtrace)	The compiler crashed. The text of the error will contain information to help Google debug the problem.
`24`	Unsupported input resource type	The resource type is not http:, and so the input file will not be retrieved.