feat(pipeline): add #length to get the command count

Closes #461

README.md

@@ -225,6 +225,13 @@ redis.pipeline([
 ]).exec(function () { /* ... */ });
 ```
 
+`#length` property shows how many commands in the pipeline:
+
+```javascript
+const length = redis.pipeline().set('foo', 'bar').get('foo').length;
+// length === 2
+```
+
 
 ## Transaction
 Most of the time, the transaction commands `multi` & `exec` are used together with pipeline.

lib/pipeline.js

@@ -31,6 +31,12 @@ function Pipeline(redis) {
     _this.resolve = resolve;
     _this.reject = reject;
   });
+
+  Object.defineProperty(this, 'length', {
+    get: function () {
+      return _this._queue.length;
+    }
+  });
 }
 
 _.assign(Pipeline.prototype, Commander.prototype);

test/functional/pipeline.js

@@ -112,7 +112,7 @@ describe('pipeline', function () {
     });
 
     it('should work', function (done) {
-      redis.pipeline().echo('foo', 'bar', '123', 'abc').exec(function(err, results) {
+      redis.pipeline().echo('foo', 'bar', '123', 'abc').exec(function (err, results) {
         expect(err).to.eql(null);
         expect(results).to.eql([
           [null, ['foo', 'bar', '123', 'abc']]
@@ -207,4 +207,19 @@ describe('pipeline', function () {
       });
     });
   });
+
+  describe('#length', function () {
+    it('return the command count', function () {
+      var redis = new Redis();
+
+      var pipeline1 = redis.pipeline().multi().set('foo', 'bar').get('foo').exec();
+      expect(pipeline1.length).to.eql(4);
+
+      var pipeline2 = redis.pipeline([
+        ['set', 'foo', 'bar'],
+        ['get', 'foo']
+      ]);
+      expect(pipeline2.length).to.eql(2);
+    });
+  });
 });