Add entryNodes function (#43)

README.md

@@ -28,6 +28,7 @@ Nodes in the graph are just simple strings with optional data associated with th
  - `directDependenciesOf(name)` - get an array containing the direct dependencies of the specified node
  - `directDependantsOf(name)` (aliased as `directDependentsOf`) - get an array containing the nodes that directly depend on the specified node
  - `overallOrder(leavesOnly)` - construct the overall processing order for the dependency graph. If `leavesOnly` is true, only nodes that do not depend on any other nodes will be returned.
+ - `entryNodes()` - array of nodes that have no dependants (i.e. nothing depends on them).
 
 Dependency Cycles are detected when running `dependenciesOf`, `dependantsOf`, and `overallOrder` and if one is found, a `DepGraphCycleError` will be thrown that includes what the cycle was in the message as well as the `cyclePath` property: e.g. `Dependency Cycle Found: a -> b -> c -> a`. If you wish to silence this error, pass `circular: true` when instantiating `DepGraph` (more below).
 
@@ -51,6 +52,7 @@ Dependency Cycles are detected when running `dependenciesOf`, `dependantsOf`, an
 
     graph.overallOrder(); // ['c', 'b', 'a']
     graph.overallOrder(true); // ['c']
+    graph.entryNodes(); // ['a']
 
     graph.addNode('d', 'data');
 

lib/dep_graph.js

@@ -324,6 +324,15 @@ DepGraph.prototype = {
 
       return result;
     }
+  },
+  /**
+   * get an array of nodes that have no dependants (i.e. nothing depends on them).
+   */
+  entryNodes: function () {
+    var self = this;
+    return Object.keys(this.nodes).filter(function (node) {
+      return self.incomingEdges[node].length === 0;
+    });
   }
 };
 

lib/index.d.ts

@@ -109,6 +109,11 @@ declare module 'dependency-graph' {
      */
     dependentsOf(name: string, leavesOnly?: boolean): string[];
 
+    /**
+     * Get an array of nodes that have no dependants (i.e. nothing depends on them).
+     */
+    entryNodes(): string[];
+
     /**
      * Construct the overall processing order for the dependency graph. If leavesOnly is true, only nodes that do not depend on any other nodes will be returned.
      * @param {boolean} leavesOnly

specs/dep_graph_spec.js

@@ -136,6 +136,19 @@ describe("DepGraph", function () {
     expect(graph.dependenciesOf("a")).toEqual(["b", "c"]);
   });
 
+  it("should find entry nodes", function () {
+    var graph = new DepGraph();
+
+    graph.addNode("a");
+    graph.addNode("b");
+    graph.addNode("c");
+
+    graph.addDependency("a", "b");
+    graph.addDependency("a", "c");
+
+    expect(graph.entryNodes()).toEqual(["a"]);
+  });
+
   it("should throw an error if a node does not exist and a dependency is added", function () {
     var graph = new DepGraph();