Added more to the Usage/ directory

Author: raghavmecheri

examples/Usage/DataLoader.md

@@ -0,0 +1,7 @@
+# The pytorchjs DataLoader class
+
+## Background
+The DataLoader class allows you to lazy-load data just as you need to pass it to your model for inference. It lets you customise a couple of things:
+- The ImageFolder class that you're passing in
+- Your batch size
+- The transforms that you would like to apply on every image you load

examples/Usage/ImageFolder.md

@@ -0,0 +1,14 @@
+# The pytorchjs ImageFolder class
+
+## Background
+The ImageFolder class is an encapsulation of an image (vision) dataset. It lets you do a couple of cool things, including:
+- Specify a custom `loader` function to load the image paths passed in. The default for this is a function that loads the image using `numjs`, which is what all our transforms expect :)
+- A transform object to be applied per image. This may be overriden if you pass this object into a DataLoader with it's own transform
+- `extensions`, a list of acceptable file extensions to load data from. The default array considered is: `[".jpg", ".jpeg", ".png", ".bmp", ".tif", ".tiff"]`
+- An `isValidFile` method to check if a file at a given path should be loaded or not.
+
+## Selective Loading
+Both `extensions` and the `isValidFile` function may be used to selectively load images from your dataset. Only one of these two parameters may be non-null. A sample isValidFile method that only selects .png images has been specified below.
+```js
+const customIsValidFile = (targetPath) => targetPath.endsWith(".png")
+```

src/torchvision/datasets/ImageFolder.js

@@ -19,22 +19,18 @@ export class ImageFolder extends DatasetFolder {
    * Create a new ImageFolder object
    * @param {string} root - The root directory to the target dataset
    * @param {Function} [defaultLoader] loader - A custom function used to load images for the ImageFolder
+   * @param {Array<String>} extensions - A list of valid extensions to load images from
    * @param {Transform} [null] transform - A transform/function used to transform source images
    * @param {Function} [null] isValidFile - Function to verifty whether a valid file is valid
    */
   constructor(
     root,
     loader = defaultLoader,
+    extensions = IMAGE_EXTENSIONS,
     transform = null,
     isValidFile = null
   ) {
-    super(
-      root,
-      loader,
-      isValidFile === null ? IMAGE_EXTENSIONS : null,
-      transform,
-      isValidFile
-    );
+    super(root, loader, extensions, transform, isValidFile);
     /**
      * A pointer to the Dataset samples
      * @type {Array.<{path: String, classIndex: Number }>}