feat: Add Object.isThenable

Currently Object.isPromise mirrors it 1:1,
but with next major we will also validate its constructor

object/ensure-promise.js

@@ -4,6 +4,6 @@ var safeToString = require("../safe-to-string")
   , isPromise    = require("./is-promise");
 
 module.exports = function (value) {
-	if (!isPromise(value)) throw new TypeError(safeToString(value) + " is not a thenable");
+	if (!isPromise(value)) throw new TypeError(safeToString(value) + " is not a promise");
 	return value;
 };

object/ensure-thenable.js

@@ -0,0 +1,9 @@
+"use strict";
+
+var safeToString = require("../safe-to-string")
+  , isThenable   = require("./is-thenable");
+
+module.exports = function (value) {
+	if (!isThenable(value)) throw new TypeError(safeToString(value) + " is not a thenable");
+	return value;
+};

object/index.js

@@ -17,6 +17,7 @@ module.exports = {
 	ensureNaturalNumberValue: require("./ensure-natural-number-value"),
 	ensurePlainFunction: require("./ensure-plain-function"),
 	ensurePromise: require("./ensure-promise"),
+	ensureThenable: require("./ensure-thenable"),
 	eq: require("./eq"),
 	every: require("./every"),
 	filter: require("./filter"),
@@ -41,6 +42,7 @@ module.exports = {
 	isPlainFunction: require("./is-plain-function"),
 	isPlainObject: require("./is-plain-object"),
 	isPromise: require("./is-promise"),
+	isThenable: require("./is-thenable"),
 	isValue: require("./is-value"),
 	keyOf: require("./key-of"),
 	keys: require("./keys"),

object/is-promise.js

@@ -1,8 +1,4 @@
 "use strict";
 
-var isCallable = require("./is-callable")
-  , isObject   = require("./is-object");
-
-module.exports = function (value) {
- return isObject(value) && isCallable(value.then);
-};
+// In next major this check will also confirm on promise constructor
+module.exports = require("./is-thenable");

object/is-thenable.js

@@ -0,0 +1,8 @@
+"use strict";
+
+var isCallable = require("./is-callable")
+  , isObject   = require("./is-object");
+
+module.exports = function (value) {
+	return isObject(value) && isCallable(value.then);
+};

test/object/ensure-thenable.js

@@ -0,0 +1,11 @@
+"use strict";
+
+module.exports = function (t, a) {
+	// Just sanity checks as proper tests are at isThenable
+	var thenable = { then: function () {} };
+
+	a.throws(function () {
+		t({});
+	}, TypeError);
+	a(t(thenable), thenable);
+};

test/object/is-thenable.js

@@ -0,0 +1,17 @@
+"use strict";
+
+module.exports = function (t, a) {
+	var promise;
+	a(t(), false);
+	a(t(null), false);
+	a(t("promise"), false);
+	a(t({}), false);
+	a(t(function () {}), false);
+	a(t({ then: {} }), false);
+	a(t({ then: function () {} }), true);
+	promise = function () {};
+	promise.then = {};
+	a(t(promise), false);
+	promise.then = function () {};
+	a(t(promise), true);
+};