Feature: useDeferred(...)

.gitignore

@@ -3,3 +3,4 @@
 node_modules/
 dist/
 coverage/
+.vscode/

src/tng-hooks.src.js

@@ -10,7 +10,7 @@
 
 	return {
 		TNG, useState, useReducer, useEffect,
-		useMemo, useCallback, useRef,
+		useMemo, useCallback, useRef, useDeferred
 	};
 
 
@@ -295,5 +295,23 @@
 		else {
 			throw new Error("useRef() only valid inside an Articulated Function or a Custom Hook.");
 		}
-	}
+  }
+
+  function useDeferred() {
+    if (getCurrentBucket()) {
+      const [deferred] = useState((function () {
+        let resolve, reject;
+        let pr = new Promise((res, rej) => {
+          resolve = res;
+          reject = rej;
+        })
+
+        return { pr, resolve, reject }
+      })())
+
+      return deferred
+    } else {
+      throw new Error("useDeferred() only valid inside an Articulated Function or a Custom Hook.")
+    }
+  }
 });

tests/tests.js

@@ -510,6 +510,69 @@ QUnit.test( "useRef(..)", function test(assert){
 	assert.strictEqual( pActual, pExpected, "call without TNG wrapping context" );
 } );
 
+QUnit.test("useDeferred(..)", function test(assert) {
+  var done = assert.async(2);
+
+  var fooExpected = [
+    "foo - setup",
+    "foo - before resolve",
+    "foo - after resolve",
+    "bar - reject",
+    "foo - resolve"
+  ]
+
+  function foo() {
+    var d = useDeferred();
+
+    assert.step("foo - setup");
+    d.pr.then(payload => {
+      assert.step(`${payload}`)
+      assert.verifySteps(fooExpected, "check order");
+      done();
+    })
+
+    assert.step("foo - before resolve");
+    d.resolve("foo - resolve")
+    assert.step("foo - after resolve")
+  }
+
+  function bar() {
+    var d = useDeferred();
+
+    d.pr.then(payload => {
+      assert.step("shouldn't hit")
+    }, err => {
+      assert.step(err)
+      done();
+    })
+
+    d.reject("bar - reject")
+  }
+
+  function baz() {
+    var d = useDeferred();
+
+    return "nope 1";
+  }
+
+  var bazExpected = "error";
+  var bazActual;
+
+  foo = TNG(foo);
+  bar = TNG(bar);
+  bar();
+  foo()
+
+  try {
+    baz();
+  } catch (err) {
+    bazActual = "error";
+  }
+
+  assert.expect(7) // note: 2 assertions + 5 `step(...)` calls
+  assert.strictEqual(bazActual, bazExpected, "call without TNG wrapping context")
+});
+
 QUnit.test( "use hooks from custom hook", function test(assert){
 	function foo() {
 		var [x,setX] = useState( -1 );