feat: thenable/ensure

README.md

@@ -568,6 +568,18 @@ isThenable({ then: () => {} }); // true
 isThenable({}); // false
 ```
 
+##### `thenable/ensure`
+
+If given argument is a thenable object, it is returned back. Otherwise `TypeError` is thrown.
+
+```javascript
+const ensureThenable = require("type/thenable/ensure");
+
+const promise = Promise.resolve();
+ensureThenable(promise); // promise
+ensureThenable({}); // Thrown TypeError: [object Object] is not a thenable object
+```
+
 ---
 
 ### Error

test/thenable/ensure.js

@@ -0,0 +1,20 @@
+"use strict";
+
+var assert         = require("chai").assert
+  , ensureThenable = require("../../thenable/ensure");
+
+describe("thenable/ensure", function () {
+	it("Should return input value", function () {
+		var value = { then: function () { return true; } };
+		assert.equal(ensureThenable(value), value);
+	});
+	it("Should crash on no value", function () {
+		try {
+			ensureThenable({});
+			throw new Error("Unexpected");
+		} catch (error) {
+			assert.equal(error.name, "TypeError");
+			assert.equal(error.message, "[object Object] is not a thenable object");
+		}
+	});
+});

thenable/ensure.js

@@ -0,0 +1,9 @@
+"use strict";
+
+var resolveException = require("../lib/resolve-exception")
+  , is               = require("./is");
+
+module.exports = function (value/*, options*/) {
+	if (is(value)) return value;
+	return resolveException(value, "%v is not a thenable object", arguments[1]);
+};