Merge pull request scala-js#38 from sjrd/add-usage

Add usage instructions and a link to the Scaladoc.

README.md

@@ -15,3 +15,99 @@ Advantages of `scalajs-bundler` over `sbt-jsdependencies` include:
 
 This repository contains `sbt-jsdependencies` for Scala.js 1.x. In Scala.js
 0.6.x, the `jsDependencies` sbt setting is part of the core distribution.
+
+# Usage
+
+Add the following line to `project/plugins.sbt`:
+
+```scala
+addSbtPlugin("org.scala-js" % "sbt-jsdependencies" % "1.0.0")
+```
+
+and enable the following plugin on Scala.js projects where you need `jsDependencies`:
+
+```scala
+enablePlugins(JSDependenciesPlugin)
+```
+
+You can write the following in the `settings` of those projects:
+
+```scala
+jsDependencies += "org.webjars" % "jquery" % "2.1.4" / "2.1.4/jquery.js"
+```
+
+This will make your project depend on the respective WebJar and include a file named `**/2.1.4/jquery.js` in the said WebJar when your project is run or tested.
+We are trying to make the semantics of "include" to be as close as possible to writing:
+
+```html
+<script type="text/javascript" src="..."></script>
+```
+
+All `jsDependencies` and associated metadata (e.g. for ordering) are persisted in a file (called `JS_DEPENDENCIES`) and shipped with the artifact your project publishes.
+For example, if you depend on the `scalajs-jquery` package for Scala.js, you do not need to explicitly depend or include `jquery.js`; this mechanism does it for you.
+
+Note: This will **not** dump the JavaScript libraries in the file containing your compiled Scala.js code as this would not work across all JavaScript virtual machines.
+However, the Scala.js plugin can generate a separate file that contains all raw JavaScript dependencies (see [below](#packageJSDependencies)).
+
+### Scoping to a Configuration
+
+You may scope `jsDependencies` on a given configuration, just like for normal `libraryDependencies`:
+
+```scala
+jsDependencies += "org.webjars" % "jquery" % "2.1.4" / "jquery.js" % "test"
+```
+
+### CommonJS name
+
+Some (most?) JavaScript libraries try to adapt the best they can to the environment in which they are being executed.
+When they do so, you have to specify explicitly the name under which they are exported in a CommonJS environment (such as Node.js), otherwise they won't work when executed in Node.js.
+This is the purpose of the `commonJSName` directive, to be used like this:
+
+```scala
+jsDependencies += "org.webjars" % "mustachejs" % "0.8.2" / "mustache.js" commonJSName "Mustache"
+```
+
+which essentially translates to a prelude
+
+```javascript
+var Mustache = require("mustache.js");
+```
+
+when running with Node.js from sbt (with `run`, `test`, etc.).
+
+### Dependency Ordering
+
+Since JavaScript does not have a class loading mechanism, the order in which libraries are loaded may matter.
+If this is the case, you can specify a library's dependencies like so:
+
+```scala
+jsDependencies += "org.webjars" % "jasmine" % "1.3.1" / "jasmine-html.js" dependsOn "jasmine.js"
+```
+
+Note that the dependee must be declared as explicit dependency elsewhere, but not necessarily in this project (for example in a project the current project depends on).
+
+### Local JavaScript Files
+
+If you need to include JavaScript files which are provided in the resources of your project, use:
+
+```scala
+jsDependencies += ProvidedJS / "myJSLibrary.js"
+```
+
+This will look for `myJSLibrary.js` in the resources and include it.
+It is an error if it doesn't exist.
+You may use ordering and scoping if you need.
+
+### Write a Dependency File
+
+If you want all JavaScript dependencies to be concatenated to a single file (for easy inclusion into a HTML file for example), you can set:
+
+```scala
+skip in packageJSDependencies := false
+```
+
+in your project settings. The resulting file in the target folder will have the suffix `-jsdeps.js`.
+
+### Scaladoc
+
+See [the Scaladoc](https://javadoc.io/doc/org.scala-js/jsdependencies-core_2.13/latest/org/scalajs/jsdependencies/core/index.html) for other configuration options.