[mixins/pushAll] efficiently push an entire array into another

src/kibana/utils/_mixins_chainable.js

@@ -295,5 +295,19 @@ define(function (require) {
 
       return list;
     },
+
+    pushAll: function (source, dest) {
+      var start = dest.length;
+      var adding = source.length;
+
+      // allocate - http://goo.gl/e2i0S0
+      dest.length = start + adding;
+
+      // fill sparse positions
+      var i = -1;
+      while (++i < adding) dest[start + i] = source[i];
+
+      return dest;
+    }
   };
 });

test/unit/specs/utils/mixins/_push_all.js

@@ -0,0 +1,15 @@
+define(function (require) {
+  return ['_.pushAll', function () {
+    var _ = require('lodash');
+
+    it('pushes an entire array into another', function () {
+      var a = [1, 2, 3, 4];
+      var b = [5, 6, 7, 8];
+
+      var output = _.pushAll(b, a);
+      expect(output).to.be(a);
+      expect(a).to.eql([1, 2, 3, 4, 5, 6, 7, 8]);
+      expect(b).to.eql([5, 6, 7, 8]);
+    });
+  }];
+});

test/unit/specs/utils/mixins/index.js

@@ -2,6 +2,7 @@ define(function (require) {
   describe('lodash mixins', function () {
     run(require('specs/utils/mixins/_move'));
     run(require('specs/utils/mixins/_organize_by'));
+    run(require('specs/utils/mixins/_push_all'));
     function run(m) { describe(m[0], m[1]); }
   });
-});
+});