install.js

install.js

makeInstaller = function (options) {
  "use strict";

  options = options || {};

¶

These file extensions will be appended to required module identifiers if they do not exactly match an installed module.
```
  var defaultExtensions = options.extensions || [".js", ".json"];
```
¶

If defined, the options.fallback function will be called when no installed module is found for a required module identifier. Often options.fallback will be implemented in terms of the native Node require function, which has the ability to load binary modules.
```
  var fallback = options.fallback;
```
¶

List of fields to look for in package.json files to determine the main entry module of the package. The first field listed here whose value is a string will be used to resolve the entry module.
```
  var mainFields = options.mainFields ||
```
¶

If options.mainFields is absent and options.browser is truthy, package resolution will prefer the “browser” field of package.json files to the “main” field. Note that this only supports string-valued “browser” fields for now, though in the future it might make sense to support the object version, a la browserify.
```
    (options.browser ? ["browser", "main"] : ["main"]);

  var hasOwn = {}.hasOwnProperty;
  function strictHasOwn(obj, key) {
    return isObject(obj) && isString(key) && hasOwn.call(obj, key);
  }
```
¶

Cache for looking up File objects given absolute module identifiers. Invariants: filesByModuleId[module.id] === fileAppendId(root, module.id) filesByModuleId[module.id].module === module
```
  var filesByModuleId = {};
```

The file object representing the root directory of the installed module tree.

  var root = new File("/", new File("/.."));
  var rootRequire = makeRequire(root);

¶

Merges the given tree of directories and module factory functions into the tree of installed modules and returns a require function that behaves as if called from a module in the root directory.
```
  function install(tree, options) {
    if (isObject(tree)) {
      fileMergeContents(root, tree, options);
    }
    return rootRequire;
  }
```

Replace this function to enable Module.prototype.prefetch.

  install.fetch = function (ids) {
    throw new Error("fetch not implemented");
  };

¶

This constructor will be used to instantiate the module objects passed to module factory functions (i.e. the third argument after require and exports), and is exposed as install.Module in case the caller of makeInstaller wishes to modify Module.prototype.
```
  function Module(id) {
    this.id = id;
```
¶

The Node implementation of module.children unfortunately includes only those child modules that were imported for the first time by this parent module (i.e., child.parent === this).
```
    this.children = [];
```
¶

This object is an install.js extension that includes all child modules imported by this module, even if this module is not the first to import them.
```
    this.childrenById = {};
  }
```
¶

Used to keep module.prefetch promise resolutions well-ordered.
```
  var lastPrefetchPromise;
```

May be shared by multiple sequential calls to module.prefetch. Initialized to {} only when necessary.

  var missing;

  Module.prototype.prefetch = function (id) {
    var module = this;
    var parentFile = getOwn(filesByModuleId, module.id);

    lastPrefetchPromise = lastPrefetchPromise || Promise.resolve();
    var previousPromise = lastPrefetchPromise;

    function walk(module) {
      var file = getOwn(filesByModuleId, module.id);
      if (fileIsDynamic(file) && ! file.pending) {
        file.pending = true;
        missing = missing || {};

¶

These are the data that will be exposed to the install.fetch callback, so it’s worth documenting each item with a comment.
```
        missing[module.id] = {
```
¶

The CommonJS module object that will be exposed to this dynamic module when it is evaluated. Note that install.fetch could decide to populate module.exports directly, instead of fetching anything. In that case, install.fetch should omit this module from the tree that it produces.
```
          module: file.module,
```
¶

List of module identifier strings imported by this module. Note that the missing object already contains all available dependencies (including transitive dependencies), so install.fetch should not need to traverse these dependencies in most cases; however, they may be useful for other reasons. Though the strings are unique, note that two different strings could resolve to the same module.
```
          deps: Object.keys(file.deps),
```
¶

The options (if any) that were passed as the second argument to the install(tree, options) function when this stub was first registered. Typically contains options.extensions, but could contain any information appropriate for the entire tree as originally installed. These options will be automatically inherited by the newly fetched modules, so install.fetch should not need to modify them.
```
          options: file.options,
```

Any stub data included in the array notation from the original entry for this dynamic module. Typically contains “main” and/or “browser” fields for package.json files, and is otherwise undefined.

          stub: file.stub
        };

        each(file.deps, function (parentId, id) {
          fileResolve(file, id);
        });

        each(module.childrenById, walk);
      }
    }

    return lastPrefetchPromise = new Promise(function (resolve) {
      var absChildId = module.resolve(id);
      each(module.childrenById, walk);
      resolve(absChildId);

    }).then(function (absChildId) {

Grab the current missing object and fetch its contents.

      var toBeFetched = missing;
      missing = null;

      function clearPending() {
        if (toBeFetched) {
          Object.keys(toBeFetched).forEach(function (id) {
            getOwn(filesByModuleId, id).pending = false;
          });
        }
      }

      return new Promise(function (resolve) {

¶

The install.fetch function takes an object mapping missing dynamic module identifiers to options objects, and should return a Promise that resolves to a module tree that can be installed. As an optimization, if there were no missing dynamic modules, then we can skip calling install.fetch entirely.
```
        resolve(toBeFetched && install.fetch(toBeFetched));

      }).then(function (tree) {
        function both() {
          install(tree);
          clearPending();
          return absChildId;
        }
```
¶

Although we want multiple install.fetch calls to run in parallel, it is important that the promises returned by module.prefetch are resolved in the same order as the original calls to module.prefetch, because previous fetches may include modules assumed to exist by more recent module.prefetch calls. Whether previousPromise was resolved or rejected, carry on with the installation regardless.
```
        return previousPromise.then(both, both);

      }, function (error) {
```

Fixes https://github.com/meteor/meteor/issues/10182.

        clearPending();
        throw error;
      });
    });
  };

  install.Module = Module;

  function getOwn(obj, key) {
    return strictHasOwn(obj, key) && obj[key];
  }

  function isObject(value) {
    return value !== null && typeof value === "object";
  }

  function isFunction(value) {
    return typeof value === "function";
  }

  function isString(value) {
    return typeof value === "string";
  }

  function makeMissingError(id) {
    return new Error("Cannot find module '" + id + "'");
  }

  Module.prototype.resolve = function (id) {
    var file = fileResolve(filesByModuleId[this.id], id);
    if (file) return file.module.id;
    var error = makeMissingError(id);
    if (fallback && isFunction(fallback.resolve)) {
      return fallback.resolve(id, this.id, error);
    }
    throw error;
  };

  Module.prototype.require = function require(id) {
    var result = fileResolve(filesByModuleId[this.id], id);
    if (result) {
      return fileEvaluate(result, this);
    }

    var error = makeMissingError(id);

    if (isFunction(fallback)) {
      return fallback(
        id, // The missing module identifier.
        this.id, // ID of the parent module.
        error // The error we would have thrown.
      );
    }

    throw error;
  };

  function makeRequire(file) {
    var module = file.module;

    function require(id) {
      return module.require(id);
    }

    require.extensions = fileGetExtensions(file).slice(0);

    require.resolve = function resolve(id) {
      return module.resolve(id);
    };

    return require;
  }

¶

File objects represent either directories or modules that have been installed. When a File respresents a directory, its .contents property is an object containing the names of the files (or directories) that it contains. When a File represents a module, its .contents property is a function that can be invoked with the appropriate (require, exports, module) arguments to evaluate the module. If the .contents property is a string, that string will be resolved as a module identifier, and the exports of the resulting module will provide the exports of the original file. The .parent property of a File is either a directory File or null. Note that a child may claim another File as its parent even if the parent does not have an entry for that child in its .contents object. This is important for implementing anonymous files, and preventing child modules from using ../relative/identifier syntax to examine unrelated modules.
```
  function File(moduleId, parent) {
    var file = this;
```

Link to the parent file.

    file.parent = parent = parent || null;

¶

The module object for this File, which will eventually boast an .exports property when/if the file is evaluated.
```
    file.module = new Module(moduleId);
    filesByModuleId[moduleId] = file;
```
¶

The .contents of the file can be either (1) an object, if the file represents a directory containing other files; (2) a factory function, if the file represents a module that can be imported; (3) a string, if the file is an alias for another file; or (4) null, if the file’s contents are not (yet) available.
```
    file.contents = null;
```

Set of module identifiers imported by this module. Note that this set is not necessarily complete, so don’t rely on it unless you know what you’re doing.

    file.deps = {};
  }

  function fileEvaluate(file, parentModule) {
    var module = file.module;
    if (! strictHasOwn(module, "exports")) {
      var contents = file.contents;
      if (! contents) {

¶

If this file was installed with array notation, and the array contained one or more objects but no functions, then the combined properties of the objects are treated as a temporary stub for file.module.exports. This is particularly important for partial package.json modules, so that the resolution logic can know the value of the “main” and/or “browser” fields, at least, even if the rest of the package.json file is not (yet) available.
```
        if (file.stub) {
          return file.stub;
        }

        throw makeMissingError(module.id);
      }

      if (parentModule) {
        module.parent = parentModule;
        var children = parentModule.children;
        if (Array.isArray(children)) {
          children.push(module);
        }
      }

      contents(
        makeRequire(file),
```

If the file had a .stub, reuse the same object for exports.

        module.exports = file.stub || {},
        module,
        file.module.id,
        file.parent.module.id
      );

      module.loaded = true;
    }

The module.runModuleSetters method will be deprecated in favor of just module.runSetters: https://github.com/benjamn/reify/pull/160

    var runSetters = module.runSetters || module.runModuleSetters;
    if (isFunction(runSetters)) {
      runSetters.call(module);
    }

    return module.exports;
  }

  function fileIsDirectory(file) {
    return file && isObject(file.contents);
  }

  function fileIsDynamic(file) {
    return file && file.contents === null;
  }

  function fileMergeContents(file, contents, options) {
    if (Array.isArray(contents)) {
      contents.forEach(function (item) {
        if (isString(item)) {
          file.deps[item] = file.module.id;
        } else if (isFunction(item)) {
          contents = item;
        } else if (isObject(item)) {
          file.stub = file.stub || {};
          each(item, function (value, key) {
            file.stub[key] = value;
          });
        }
      });

      if (! isFunction(contents)) {

If the array did not contain a function, merge nothing.

        contents = null;
      }

    } else if (! isFunction(contents) &&
               ! isString(contents) &&
               ! isObject(contents)) {

If contents is neither an array nor a function nor a string nor an object, just give up and merge nothing.

      contents = null;
    }

    if (contents) {
      file.contents = file.contents || (isObject(contents) ? {} : contents);
      if (isObject(contents) && fileIsDirectory(file)) {
        each(contents, function (value, key) {
          if (key === "..") {
            child = file.parent;

          } else {
            var child = getOwn(file.contents, key);

            if (! child) {
              child = file.contents[key] = new File(
                file.module.id.replace(/\/*$/, "/") + key,
                file
              );

              child.options = options;
            }
          }

          fileMergeContents(child, value, options);
        });
      }
    }
  }

  function each(obj, callback, context) {
    Object.keys(obj).forEach(function (key) {
      callback.call(this, obj[key], key);
    }, context);
  }

  function fileGetExtensions(file) {
    return file.options
      && file.options.extensions
      || defaultExtensions;
  }

  function fileAppendIdPart(file, part, extensions) {

Always append relative to a directory.

    while (file && ! fileIsDirectory(file)) {
      file = file.parent;
    }

    if (! file || ! part || part === ".") {
      return file;
    }

    if (part === "..") {
      return file.parent;
    }

    var exactChild = getOwn(file.contents, part);

Only consider multiple file extensions if this part is the last part of a module identifier and not equal to . or .., and there was no exact match or the exact match was a directory.

    if (extensions && (! exactChild || fileIsDirectory(exactChild))) {
      for (var e = 0; e < extensions.length; ++e) {
        var child = getOwn(file.contents, part + extensions[e]);
        if (child && ! fileIsDirectory(child)) {
          return child;
        }
      }
    }

    return exactChild;
  }

  function fileAppendId(file, id, extensions) {
    var parts = id.split("/");

Use Array.prototype.every to terminate iteration early if fileAppendIdPart returns a falsy value.

    parts.every(function (part, i) {
      return file = i < parts.length - 1
        ? fileAppendIdPart(file, part)
        : fileAppendIdPart(file, part, extensions);
    });

    return file;
  }

  function recordChild(parentModule, childFile) {
    var childModule = childFile && childFile.module;
    if (parentModule && childModule) {
      parentModule.childrenById[childModule.id] = childModule;
    }
  }

  function fileResolve(file, id, parentModule, seenDirFiles) {
    var parentModule = parentModule || file.module;
    var extensions = fileGetExtensions(file);

    file =

¶

Absolute module identifiers (i.e. those that begin with a / character) are interpreted relative to the root directory, which is a slight deviation from Node, which has access to the entire file system.
```
      id.charAt(0) === "/" ? fileAppendId(root, id, extensions) :
```
¶

Relative module identifiers are interpreted relative to the current file, naturally.
```
      id.charAt(0) === "." ? fileAppendId(file, id, extensions) :
```
¶

Top-level module identifiers are interpreted as referring to packages in node_modules directories.
```
      nodeModulesLookup(file, id, extensions);
```
¶

If the identifier resolves to a directory, we use the same logic as Node to find an index.js or package.json file to evaluate.
```
    while (fileIsDirectory(file)) {
      seenDirFiles = seenDirFiles || [];
```

If the “main” field of a package.json file resolves to a directory we’ve already considered, then we should not attempt to read the same package.json file again. Using an array as a set is acceptable here because the number of directories to consider is rarely greater than 1 or 2. Also, using indexOf allows us to store File objects instead of strings.

      if (seenDirFiles.indexOf(file) < 0) {
        seenDirFiles.push(file);

        var pkgJsonFile = fileAppendIdPart(file, "package.json"), main;
        var pkg = pkgJsonFile && fileEvaluate(pkgJsonFile, parentModule);
        if (pkg &&
            mainFields.some(function (name) {
              return isString(main = pkg[name]);
            })) {

The “main” field of package.json does not have to begin with ./ to be considered relative, so first we try simply appending it to the directory path before falling back to a full fileResolve, which might return a package from a node_modules directory.

          var mainFile = fileAppendId(file, main, extensions) ||
            fileResolve(file, main, parentModule, seenDirFiles);

          if (mainFile) {
            file = mainFile;
            recordChild(parentModule, pkgJsonFile);

¶

The fileAppendId call above may have returned a directory, so continue the loop to make sure we resolve it to a non-directory file.
```
            continue;
          }
        }
      }
```

If we didn’t find a package.json file, or it didn’t have a resolvable .main property, the only possibility left to consider is that this directory contains an index.js module. This assignment almost always terminates the while loop, because there’s very little chance fileIsDirectory(file) will be true for fileAppendIdPart(file, "index", extensions). However, in principle it is remotely possible that a file called index.js could be a directory instead of a file.

      file = fileAppendIdPart(file, "index", extensions);
    }

    if (file && isString(file.contents)) {
      file = fileResolve(file, file.contents, parentModule, seenDirFiles);
    }

    recordChild(parentModule, file);

    return file;
  };

  function nodeModulesLookup(file, id, extensions) {
    for (var resolved; file && ! resolved; file = file.parent) {
      resolved = fileIsDirectory(file) &&
        fileAppendId(file, "node_modules/" + id, extensions);
    }
    return resolved;
  }

  return install;
};

if (typeof exports === "object") {
  exports.makeInstaller = makeInstaller;
}