webpack/examples/loader/README.md

example.js

// Polyfill require for node.js usage of loaders
require = require("../../require-polyfill")(require.valueOf());

// use our loader
console.dir(require("./loader!./file"));

// use buildin json loader
console.dir(require("./test.json")); // default by extension
console.dir(require("json!./test.json")); // manual

file.js

exports.foo = "bar";

loader.js

module.exports = function(contents, options, callback) {
	
	if(contents.length !== 1)
		throw new Error("loader takes exactly one file as parameter");
	
	if(callback) {
		// compile for web
		callback(null /* no error */, 
			"exports.answer = 42;\n" + 
			contents[0]);
	} else {
		// execute for node.js
		var Module = require("module");
		var m = new Module(options.request);
		m.exports.answer = 42;
		m._compile(contents[0], options.filename);
		return m.exports;
	}

}

test.json

{
	"foobar": 1234
}

js/output.js

/******/(function(modules) {
/******/	var installedModules = {};
/******/	function require(moduleId) {
/******/		if(typeof moduleId !== "number") throw new Error("Cannot find module '"+moduleId+"'");
/******/		if(installedModules[moduleId])
/******/			return installedModules[moduleId].exports;
/******/		var module = installedModules[moduleId] = {
/******/			exports: {}
/******/		};
/******/		modules[moduleId](module, module.exports, require);
/******/		return module.exports;
/******/	}
/******/	require.ensure = function(chunkId, callback) {
/******/		callback(require);
/******/	};
/******/	return require(0);
/******/})
/******/({
/******/0: function(module, exports, require) {

/******/ /* WEBPACK FREE VAR INJECTION */ (function(console) {
// Polyfill require for node.js usage of loaders
require = require(/* ../../require-polyfill */1)(require.valueOf());

// use our loader
console.dir(require(/* ./loader!./file */3));

// use buildin json loader
console.dir(require(/* ./test.json */4)); // default by extension
console.dir(require(/* json!./test.json */4)); // manual
/******/ /* WEBPACK FREE VAR INJECTION */ }(require(/* __webpack_console */2)))

/******/},
/******/
/******/1: function(module, exports, require) {

// No polyfill needed when compiled with webpack
module.exports = function(r){return r}

/******/},
/******/
/******/2: function(module, exports, require) {

var console = window.console;
module.exports = console;
for(var name in {log:1, info:1, error:1, warn:1, dir:1, trace:1, assert:1})
	if(!console[name])
		console[name] = function() {};
if(!console.time)
console.time = function(label) {
	times[label] = Date.now();
};
if(!console.timeEnd)
console.timeEnd = function() {
	var duration = Date.now() - times[label];
	console.log('%s: %dms', label, duration);
};

/******/},
/******/
/******/3: function(module, exports, require) {



/******/},
/******/
/******/4: function(module, exports, require) {

module.exports = {
	"foobar": 1234
}

/******/},
/******/
/******/})

Console output

Prints in node.js (node example.js) and in browser:

{ answer: 42, foo: 'bar' }
{ foobar: 1234 }
{ foobar: 1234 }

Info

Uncompressed

Chunks: 1
Modules: 5
Modules including duplicates: 5
Modules pre chunk: 5
Modules first chunk: 5
     output.js:     2048 characters
output.js
    0 .\example.js
       main
    1 (webpack)\require-polyfill.web.js
       require (1x) from .\example.js
    2 (webpack)\buildin\__webpack_console.js
       require (3x) from .\example.js
    3 .\loader.js!.\file.js
       require (1x) from .\example.js
    4 (webpack)\node_modules\json-loader\index.js!.\test.json
       require (1x) from .\example.js
       require (1x) from .\example.js