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I have a Node.js project that I want to pile with Closure Compiler. I do not want it to run in the browser/use browserify. I mainly want the utility of type checking. I originally got the piler to work correctly using the following:

java -jar piler.jar -W VERBOSE 
                       --language_in ECMASCRIPT5_STRICT 
                       --externs closure-externs.js 
                       --js="lib/**.js"

Where closure-externs.js manually defined variables and functions which I was using from Node.js in a rather crude way:

// closure-externs.js

/** @constructor */function Buffer(something){}
function require(path){}
var process = {};
[...]

It turns out that this worked only through sheer luck. There is no dependency tracking between files, so you can have cases where you return a type {Foo} and the piler will plain that it doesn't exist (depending on the machine, depending on the pile order). I then found out I was doing it all wrong and should be using --process_mon_js_modules so the piler will do dependency tracking where I require("foo"). I am currently invoking the piler like so:

java -jar piler.jar -W VERBOSE 
                       --language_in ECMASCRIPT5_STRICT 
                       --externs externs/fs.js 
                       --js="lib/**.js"
                       --process_mon_js_modules 
                       --mon_js_entry_module app.js

But this is failing with:

 ERROR - required entry point "module$crypto" never provided
 ERROR - required entry point "module$dgram" never provided
 ERROR - required entry point "module$extend" never provided
 ERROR - required entry point "module$fs" never provided
 ERROR - required entry point "module$net" never provided
 ERROR - required entry point "module$q" never provided

Some of these modules are native to Node.js (e.g. fs) whereas others are contained in node_modules like q. I don't want to run these external modules through the piler, so I know I need to set up externs file(s) for them. I know there is .js-closure-piler-externs for mon Node.js externs, and I know how to invoke them on the piler, but for some reason when I do something like --externs externs/fs.js the error for module$fs remains. What am I doing wrong?

I know there's other flags like --module and --mon_js_module_path_prefix but I'm not sure if I need to use them to get this to work or not. My Google-fu has failed to e up with any answers on the correct incantation here. :(

I have a Node.js project that I want to pile with Closure Compiler. I do not want it to run in the browser/use browserify. I mainly want the utility of type checking. I originally got the piler to work correctly using the following:

java -jar piler.jar -W VERBOSE 
                       --language_in ECMASCRIPT5_STRICT 
                       --externs closure-externs.js 
                       --js="lib/**.js"

Where closure-externs.js manually defined variables and functions which I was using from Node.js in a rather crude way:

// closure-externs.js

/** @constructor */function Buffer(something){}
function require(path){}
var process = {};
[...]

It turns out that this worked only through sheer luck. There is no dependency tracking between files, so you can have cases where you return a type {Foo} and the piler will plain that it doesn't exist (depending on the machine, depending on the pile order). I then found out I was doing it all wrong and should be using --process_mon_js_modules so the piler will do dependency tracking where I require("foo"). I am currently invoking the piler like so:

java -jar piler.jar -W VERBOSE 
                       --language_in ECMASCRIPT5_STRICT 
                       --externs externs/fs.js 
                       --js="lib/**.js"
                       --process_mon_js_modules 
                       --mon_js_entry_module app.js

But this is failing with:

 ERROR - required entry point "module$crypto" never provided
 ERROR - required entry point "module$dgram" never provided
 ERROR - required entry point "module$extend" never provided
 ERROR - required entry point "module$fs" never provided
 ERROR - required entry point "module$net" never provided
 ERROR - required entry point "module$q" never provided

Some of these modules are native to Node.js (e.g. fs) whereas others are contained in node_modules like q. I don't want to run these external modules through the piler, so I know I need to set up externs file(s) for them. I know there is https://github./dcodeIO/node.js-closure-piler-externs for mon Node.js externs, and I know how to invoke them on the piler, but for some reason when I do something like --externs externs/fs.js the error for module$fs remains. What am I doing wrong?

I know there's other flags like --module and --mon_js_module_path_prefix but I'm not sure if I need to use them to get this to work or not. My Google-fu has failed to e up with any answers on the correct incantation here. :(

• javascript
• node.js
• google-closure-piler

Share Improve this question Follow asked May 15, 2015 at 13:55 DororoDororo 3,44022 gold badges3333 silver badges4848 bronze badges 3

• 2 Many of the externs you need are officially maintained in the piler project: github./google/closure-piler/tree/master/contrib/nodejs. The contrib externs are now also distributed as part of the official npm package for the piler: npmjs./package/google-closure-piler – Chad Killingsworth Commented May 15, 2015 at 14:41
• I know these files exist. My question is how do I use these files correctly with piler.jar as --externs doesn't seem to be working as I think it should. – Dororo Commented May 15, 2015 at 17:30
• That's why I posted it as a ment - I'm interested in an answer as well. – Chad Killingsworth Commented May 15, 2015 at 18:56

Add a ment  | 

2 Answers 2

Sorted by: Reset to default 6 +100

The issue is that you wish for the piler to somehow recognize that certain require calls are internal, namely that the required module should be processed by the piler as source, and others are external so should be left alone. There isn't a good way to handle this situation currently.

Workarounds

Use Post-processing to Add External Require Statements

In this scenario you would pletely omit any require statements to external modules. The piler would only process code with internal require statements and modules. After pilation, you would prepend the external require statements:

Header JS To Be Prepended

var crypto = require('crypto');

Source To Be Compiled

console.log(crypto);

Because crypto is declared in an extern, the piler will correctly recognize the type and symbol name.

Alias Require Calls

When the --process_mon_js_modules is specified, the piler recognizes require statements and expands them in a similar fashion to the way macros work in other languages. By aliasing the require statements that should remain external, the piler will not recognize them and thus not expand them.

Source To Be Compiled

var externalRequire = require;
/** @suppress {duplicate} this is already defined in externs */
var crypto = externalRequire('crypto');
console.log(crypto)

If you're using the Closure Compiler only for type-checking—i.e., with the --checks-only option—there is another workaround which has the advantage (over the ones mentioned in Chad's answer) of working correctly with unmodified third-party NPM modules which in turn import built-in modules.

Using Stubs

The trick is to create stub NPM modules to stand in for the built-in ones. These can be minimal; they only need to declare the parts of the API you're actually using.

Here's an example for the path built-in module.

In externs/path/path.js I have the "externs" declarations (not actually externs, so e.g. you can't use @nosideeffects) for the part of path that I need:

/** @const */
var path = {};

/**
 * @param {string} path
 * @return {string}
 */
path.dirname = function(path) {};

/**
 * @param {string} path
 * @return {string}
 */
path.extname = function(path) {};

/**
 * @param {...string} var_args
 * @return {string}
 */
path.join = function(var_args) {};

module.exports = path;

In externs/path/package.json, I have a minimal NPM package config:

{
  "description": "Fake package.json for require('path')",
  "main": "path.js",
  "name": "path",
}

Then create a symlink from node_modules/path to externs/path, and add the following to my piler flags:

node_modules/path/package.json
node_modules/path/path.js

(You could put the stub implementation directly in to node_modules but I prefer to keep my stubs separate from the real modules managed by npm. I just need to remember to manually add the symlinks to my Git repo, because it's otherwise configured to ignore node_modules.)

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