feature: Add isAsyncIterable function

src/index.js

@@ -10,6 +10,7 @@ export { default as isNotNull } from './isNotNull';
 export { default as isNotNil } from './isNotNil';
 export { default as isArray } from './isArray';
 export { default as isIterable } from './isIterable';
+export { default as isAsyncIterable } from './isAsyncIterable';
 export { default as isEmptyArray } from './isEmptyArray';
 export { default as isNotArray } from './isNotArray';
 export { default as isNonEmptyArray } from './isNonEmptyArray';

src/isAsyncIterable.js

@@ -0,0 +1,41 @@
+import { hasIn, curryN } from 'ramda';
+
+import isFunction from './isFunction';
+
+/**
+ * Checks whether the passed value is async iterable.
+ *
+ * @func isAsyncIterable
+ * @memberOf RA
+ * @since {@link https://char0n.github.io/ramda-adjunct/3.2.0|v3.2.0}
+ * @category Type
+ * @sig * -> Boolean
+ * @param {*} val The value to test
+ * @see {@link https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Symbol/asyncIterator}
+ * @return {boolean}
+ * @example
+ *
+ * RA.isAsyncIterable({
+ *   async* [Symbol.asyncIterator]() {
+ *       yield "Blade";
+ *       yield "Runner"
+ *   }
+ * }); //=> true
+ *
+ * RA.isAsyncIterable({}); //=> false
+ * RA.isAsyncIterable(-0); //=> false
+ * RA.isAsyncIterable(null); //=> false
+ * RA.isAsyncIterable(undefined); //=> false
+ */
+const isAsyncIterable = curryN(1, (val) => {
+  if (typeof Symbol === 'undefined') {
+    return false;
+  }
+
+  return (
+    hasIn(Symbol.asyncIterator, Object(val)) &&
+    isFunction(val[Symbol.asyncIterator])
+  );
+});
+
+export default isAsyncIterable;

test/isAsyncIterable.js

@@ -0,0 +1,89 @@
+import { assert } from 'chai';
+import * as R from 'ramda';
+
+import * as RA from '../src';
+
+describe('isAsyncIterable', function () {
+  context('given the item is an array with items', function () {
+    specify('should return false', function () {
+      assert.isFalse(RA.isAsyncIterable(['arrays', 'are', 'iterable']));
+    });
+  });
+
+  context(
+    'given the item is an Object implementing an asyncIterator',
+    function () {
+      specify('should return true', function () {
+        const asyncIterable = {
+          async *[Symbol.asyncIterator]() {
+            yield 'Blade';
+            yield 'Runner';
+          },
+        };
+        assert.isTrue(RA.isAsyncIterable(asyncIterable));
+      });
+    }
+  );
+
+  context('given the value undefined', function () {
+    specify('should return false', function () {
+      assert.isFalse(RA.isAsyncIterable(undefined));
+    });
+  });
+
+  context('given a number', function () {
+    specify('should return false', function () {
+      assert.isFalse(RA.isAsyncIterable(42));
+    });
+  });
+
+  context('given the value null', function () {
+    specify('should return false', function () {
+      assert.isFalse(RA.isAsyncIterable(null));
+    });
+  });
+
+  context('given the value NaN', function () {
+    specify('should return false', function () {
+      assert.isFalse(RA.isAsyncIterable(NaN));
+    });
+  });
+
+  context('given the value Infinity', function () {
+    specify('should return false', function () {
+      assert.isFalse(RA.isAsyncIterable(Infinity));
+    });
+  });
+
+  context('given a boolean value', function () {
+    specify('should return false', function () {
+      assert.isFalse(RA.isAsyncIterable(true));
+    });
+  });
+
+  context('given the value -0', function () {
+    specify('should return false', function () {
+      assert.isFalse(RA.isAsyncIterable(-0));
+    });
+  });
+
+  context('given an empty object', function () {
+    specify('should return false', function () {
+      assert.isFalse(RA.isAsyncIterable({}));
+    });
+  });
+
+  context('should support placeholder to specify "gaps"', function () {
+    specify('should return false', function () {
+      const isAsyncIterable = RA.isAsyncIterable(R.__);
+      const asyncIterable = {
+        async *[Symbol.asyncIterator]() {
+          yield 'Blade';
+          yield 'Runner';
+        },
+      };
+
+      assert.isTrue(isAsyncIterable(asyncIterable));
+    });
+  });
+});