Concepts

Files

Defiler's concept of a file is something that can come from one of two places: a physical file on the disk, or a virtual file that is generated by your code. These two types of files differ very slightly in how they are treated, but for the most part Defiler handles them both the same.

Files have a path property containing the relative path to the file, as well as dir, filename, and ext properties containing portions of the path. All of these can be updated and keep the others in sync. paths contains an array of all historical paths this File instance has had since its creation.

For physical files, the stats property contains the fs.Stats object retrieved for the original file.

Files also have text and bytes properties, containing string and Buffer representations of the file's contents. Either can be updated and keeps the other in sync. (You shouldn't mutate bytes, only reassign it.) The enc property specifies the encoding to be used when converting between text and bytes, and can be changed.

See the API docs for more information.

The transform

Every file (physical and virtual) is run through the transform function you register with Defiler. The transform mutates the object representing the file in-place, and returns a promise indicating when it's finished.

The transform is called, for each file, with an object containing defiler (the Defiler instance) and file (the File instance). The transform should mutate the file object as it sees fit. It can also take whichever actions it wishes based on the file (including, for example, writing output to disk). Files' paths can be changed as they're transformed, but the main way to refer to them from other files will continue to be by their original path (see dependence).

Dependence

Files can be made to depend on other files, so that changes to a dependency cause the dependent to be re-transformed. For physical files, the file does not need to be re-read from the disk before it can be re-transformed, as the original version is kept in memory.

The defiler.get(path) method, when used inside the transform, lets you depend on and retrieve other transformed files. It should be passed the original path of a file, and will return a Promise resolving to the transformed File instance. If the requested file does not exist (or if you have a deadlock via a system of mutually-depending files, none of which will continue transforming until another one finishes), the Promise will resolve to undefined.

The defiler.get method can also be passed an array of (original) paths, in which case it will return a Promise resolving to an array of File instances (or undefineds).

See the API docs for more information.

Virtual files

During the transform's processing of a file, you can also create virtual files, which don't directly correspond one-to-one with physical files. The Defiler instance has a defiler.add(file) method, which you can pass a File instance to (or a POJO, which will be turned into a File). The virtual file will run through the transform and will thereafter be treated pretty much like a physical file. In particular, you can make other files depend on it with defiler.get(path).

Since Defiler has no way of knowing which virtual files will be created from transforming which files, when defiler.get is used to request a file that doesn't exist yet, Defiler waits until it does. Requesting a file that's never going to exist would cause a deadlock, so Defiler resolves this as a generalization of the above-mentioned deadlock resolution: If it ever happens that every in-process action is waiting for some other transformed file to exist, Defiler will resolve each of those pending Promises returned by defiler.get to undefined.

Generators

Generators are an independent way of interacting with the Defiler instance, for things that do not fit well into the main transform. Each generator is a function that accepts one argument, an object containing defiler. A generator would typically call defiler.get and/or defiler.add to retrieve dependencies and write new virtual files. Automatic dependence handling also works here, so when one of the files retrieved by defiler.get changes, that generator will be re-run.

It's beneficial to write multiple smaller generators, rather than a single large one. This helps ensure that unneeded recalculation is not done when a file changes.

Usage

First, create a new Defiler instance, initializing it with the directory to watch, the transform, and the generators.

Then, call its exec() method to set everything in motion. This returns a Promise that will resolve when the initial wave of processing has completed.

Useful things available on the Defiler instance for you to use in the transform or the generators are:

defiler.paths - a Set of the paths of all of the physical files
defiler.files - a Map of original paths to the transformed File instances
defiler.get(path) - a method to retrieve one or more transformed Files based on their original paths
defiler.add(file) - a method to add a virtual file, which is then transformed like a physical one is, and which can be depended on by other files

In closing

See the API docs for more information, and for a couple of other things not covered here.

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