webpack/examples/loader

example.js

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

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

file.js

exports.foo = "bar";

loader.js

module.exports = function(content) {
	return "exports.answer = 42;\n" + content;
}

test.css

.some-class {
	color: hotpink;
}

dist/output.js

/******/ (function(modules) { /* webpackBootstrap */ })

/******/ (function(modules, runtime) { // webpackBootstrap
/******/ 	"use strict";
/******/ 	// The module cache
/******/ 	var installedModules = {};
/******/
/******/ 	// The require function
/******/ 	function __webpack_require__(moduleId) {
/******/
/******/ 		// Check if module is in cache
/******/ 		if(installedModules[moduleId]) {
/******/ 			return installedModules[moduleId].exports;
/******/ 		}
/******/ 		// Create a new module (and put it into the cache)
/******/ 		var module = installedModules[moduleId] = {
/******/ 			i: moduleId,
/******/ 			l: false,
/******/ 			exports: {}
/******/ 		};
/******/
/******/ 		// Execute the module function
/******/ 		modules[moduleId].call(module.exports, module, module.exports, __webpack_require__);
/******/
/******/ 		// Flag the module as loaded
/******/ 		module.l = true;
/******/
/******/ 		// Return the exports of the module
/******/ 		return module.exports;
/******/ 	}
/******/
/******/
/******/
/******/ 	// the startup function
/******/ 	function startup() {
/******/ 		// Load entry module and return exports
/******/ 		return __webpack_require__(0);
/******/ 	};
/******/
/******/ 	// run startup
/******/ 	return startup();
/******/ })
/************************************************************************/

/******/ ([
/* 0 */
/*!********************!*\
  !*** ./example.js ***!
  \********************/
/*! other exports [maybe provided (runtime-defined)] [no usage info] */
/*! runtime requirements: __webpack_require__ */
/***/ (function(__unusedmodule, __unusedexports, __webpack_require__) {

// use our loader
console.dir(__webpack_require__(/*! ./loader!./file */ 1));

// use buildin css loader
console.dir(__webpack_require__(/*! ./test.css */ 2)); // default by extension
console.dir(__webpack_require__(/*! css-loader!./test.css */ 2)); // manual


/***/ }),
/* 1 */
/*!*****************************!*\
  !*** ./loader.js!./file.js ***!
  \*****************************/
/*! other exports [maybe provided (runtime-defined)] [no usage info] */
/*! runtime requirements: __webpack_exports__ */
/***/ (function(__unusedmodule, exports) {

exports.answer = 42;
exports.foo = "bar";

/***/ }),
/* 2 */
/*!****************************************************************!*\
  !*** (webpack)/node_modules/css-loader/dist/cjs.js!./test.css ***!
  \****************************************************************/
/*! other exports [maybe provided (runtime-defined)] [no usage info] */
/*! runtime requirements: __webpack_exports__module, __webpack_require__,  */
/***/ (function(module, exports, __webpack_require__) {

exports = module.exports = __webpack_require__(/*! ../../node_modules/css-loader/dist/runtime/api.js */ 3)(false);
// Module
exports.push([module.i, ".some-class {\n\tcolor: hotpink;\n}\n", ""]);



/***/ }),
/* 3 */
/*!*************************************************************!*\
  !*** (webpack)/node_modules/css-loader/dist/runtime/api.js ***!
  \*************************************************************/
/*! other exports [maybe provided (runtime-defined)] [no usage info] */
/*! runtime requirements: module */
/***/ (function(module) {

"use strict";


/*
  MIT License http://www.opensource.org/licenses/mit-license.php
  Author Tobias Koppers @sokra
*/
// css base code, injected by the css-loader
module.exports = function (useSourceMap) {
  var list = []; // return the list of modules as css string

  list.toString = function toString() {
    return this.map(function (item) {
      var content = cssWithMappingToString(item, useSourceMap);

      if (item[2]) {
        return '@media ' + item[2] + '{' + content + '}';
      } else {
        return content;
      }
    }).join('');
  }; // import a list of modules into the list


  list.i = function (modules, mediaQuery) {
    if (typeof modules === 'string') {
      modules = [[null, modules, '']];
    }

    var alreadyImportedModules = {};

    for (var i = 0; i < this.length; i++) {
      var id = this[i][0];

      if (id != null) {
        alreadyImportedModules[id] = true;
      }
    }

    for (i = 0; i < modules.length; i++) {
      var item = modules[i]; // skip already imported module
      // this implementation is not 100% perfect for weird media query combinations
      // when a module is imported multiple times with different media queries.
      // I hope this will never occur (Hey this way we have smaller bundles)

      if (item[0] == null || !alreadyImportedModules[item[0]]) {
        if (mediaQuery && !item[2]) {
          item[2] = mediaQuery;
        } else if (mediaQuery) {
          item[2] = '(' + item[2] + ') and (' + mediaQuery + ')';
        }

        list.push(item);
      }
    }
  };

  return list;
};

function cssWithMappingToString(item, useSourceMap) {
  var content = item[1] || '';
  var cssMapping = item[3];

  if (!cssMapping) {
    return content;
  }

  if (useSourceMap && typeof btoa === 'function') {
    var sourceMapping = toComment(cssMapping);
    var sourceURLs = cssMapping.sources.map(function (source) {
      return '/*# sourceURL=' + cssMapping.sourceRoot + source + ' */';
    });
    return [content].concat(sourceURLs).concat([sourceMapping]).join('\n');
  }

  return [content].join('\n');
} // Adapted from convert-source-map (MIT)


function toComment(sourceMap) {
  // eslint-disable-next-line no-undef
  var base64 = btoa(unescape(encodeURIComponent(JSON.stringify(sourceMap))));
  var data = 'sourceMappingURL=data:application/json;charset=utf-8;base64,' + base64;
  return '/*# ' + data + ' */';
}

/***/ })
/******/ ]);

Console output

Prints in node.js (enhanced-require example.js) and in browser:

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

Info

Unoptimized

Hash: 0a1b2c3d4e5f6a7b8c9d
Version: webpack 5.0.0-alpha.11
    Asset      Size  Chunks             Chunk Names
output.js  5.45 KiB     {0}  [emitted]  main
Entrypoint main = output.js
chunk {0} output.js (main) 2.76 KiB [entry] [rendered]
    > ./example.js main
 [0] ./example.js 204 bytes {0} [built]
     [used exports unknown]
     entry ./example.js main
 [1] ./loader.js!./file.js 41 bytes {0} [built]
     [used exports unknown]
     cjs require ./loader!./file [0] ./example.js 2:12-38
 [2] (webpack)/node_modules/css-loader/dist/cjs.js!./test.css 179 bytes {0} [built]
     [used exports unknown]
     cjs require ./test.css [0] ./example.js 5:12-33
     cjs require !css-loader!./test.css [0] ./example.js 6:12-45
 [3] (webpack)/node_modules/css-loader/dist/runtime/api.js 2.35 KiB {0} [built]
     [used exports unknown]
     cjs require ../../node_modules/css-loader/dist/runtime/api.js [2] (webpack)/node_modules/css-loader/dist/cjs.js!./test.css 1:27-87

Production mode

Hash: 0a1b2c3d4e5f6a7b8c9d
Version: webpack 5.0.0-alpha.11
    Asset      Size  Chunks             Chunk Names
output.js  1.17 KiB   {179}  [emitted]  main
Entrypoint main = output.js
chunk {179} output.js (main) 2.76 KiB [entry] [rendered]
    > ./example.js main
  [90] (webpack)/node_modules/css-loader/dist/cjs.js!./test.css 179 bytes {179} [built]
       cjs require ./test.css [144] ./example.js 5:12-33
       cjs require !css-loader!./test.css [144] ./example.js 6:12-45
 [144] ./example.js 204 bytes {179} [built]
       entry ./example.js main
 [232] ./loader.js!./file.js 41 bytes {179} [built]
       cjs require ./loader!./file [144] ./example.js 2:12-38
 [609] (webpack)/node_modules/css-loader/dist/runtime/api.js 2.35 KiB {179} [built]
       cjs require ../../node_modules/css-loader/dist/runtime/api.js [90] (webpack)/node_modules/css-loader/dist/cjs.js!./test.css 1:27-87