Merge pull request #109 from facebook/return-method

Implement generator.return(argument) method for closing generators.

Now officially part of the ES6 spec: https://people.mozilla.org/~jorendorff/es6-draft.html#sec-generator.prototype.return

runtime/dev.js

@@ -140,6 +140,9 @@
             method = "next";
             arg = undefined;
           }
+
+        } else if (method === "return") {
+          context.abrupt("return", arg);
         }
 
         state = GenStateExecuting;
@@ -182,6 +185,7 @@
 
     generator.next = invoke.bind(generator, "next");
     generator.throw = invoke.bind(generator, "throw");
+    generator.return = invoke.bind(generator, "return");
 
     return generator;
   }

test/tests.es6.js

@@ -1797,3 +1797,51 @@ describe("for-of loops", function() {
     ], 6);
   });
 });
+
+describe("generator return method", function() {
+  if (!runningInTranslation) {
+    // The return method has not been specified or implemented natively,
+    // yet, so these tests need only pass in translation.
+    return;
+  }
+
+  it("should work with newborn generators", function() {
+    function *gen() {
+      yield 0;
+    }
+
+    var g = gen();
+
+    assert.deepEqual(g.return("argument"), {
+      value: "argument",
+      done: true
+    });
+
+    assertAlreadyFinished(g);
+  });
+
+  it("should behave as if generator actually returned", function() {
+    var executedFinally = false;
+
+    function *gen() {
+      try {
+        yield 0;
+      } catch (err) {
+        assert.ok(false, "should not have executed the catch handler");
+      } finally {
+        executedFinally = true;
+      }
+    }
+
+    var g = gen();
+    assert.deepEqual(g.next(), { value: 0, done: false });
+
+    assert.deepEqual(g.return("argument"), {
+      value: "argument",
+      done: true
+    });
+
+    assert.strictEqual(executedFinally, true);
+    assertAlreadyFinished(g);
+  });
+});