From d50148591b9a8bf7a49f873e1eaf5f8af364cb70 Mon Sep 17 00:00:00 2001
From: Sebastian Markbage <sema@fb.com>
Date: Tue, 2 Jul 2013 18:26:54 -0700
Subject: [PATCH] Introduce a supported way to slice children

Introduces a counterpart to mapChildren. It excludes empty children just as
mapChildren for compatibility. With might introduce something like
sliceChildrenIncludingEmptyValues at some point.
---
 src/utils/__tests__/sliceChildren-test.js | 119 ++++++++++++++++++++++
 src/utils/sliceChildren.js                |  59 +++++++++++
 2 files changed, 178 insertions(+)
 create mode 100644 src/utils/__tests__/sliceChildren-test.js
 create mode 100644 src/utils/sliceChildren.js

diff --git a/src/utils/__tests__/sliceChildren-test.js b/src/utils/__tests__/sliceChildren-test.js
new file mode 100644
index 0000000..8ff3b95
--- /dev/null
+++ b/src/utils/__tests__/sliceChildren-test.js
@@ -0,0 +1,119 @@
+/**
+ * Copyright 2013 Facebook, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ * @emails react-core
+ * @jsx React.DOM
+ */
+
+"use strict";
+
+describe('sliceChildren', function() {
+
+  var React;
+  var ReactTestUtils;
+
+  var sliceChildren;
+  var reactComponentExpect;
+
+  var Partial;
+
+  beforeEach(function() {
+    React = require('React');
+    ReactTestUtils = require('ReactTestUtils');
+
+    sliceChildren = require('sliceChildren');
+    reactComponentExpect = require('reactComponentExpect');
+
+    Partial = React.createClass({
+      render: function() {
+        return (
+          <div>
+            {sliceChildren(
+              this.props.children,
+              this.props.start,
+              this.props.end
+            )}
+          </div>
+        );
+      }
+    });
+  });
+
+  function renderAndSlice(set, start, end) {
+    var instance = <Partial start={start} end={end}>{set}</Partial>;
+    ReactTestUtils.renderIntoDocument(instance);
+    var rendered = reactComponentExpect(instance)
+      .expectRenderedChild()
+      .instance();
+    return rendered.props.children;
+  }
+
+  it('should render the whole set if start zero is supplied', function() {
+    var fullSet = [
+      <div key="A" />,
+      <div key="B" />,
+      <div key="C" />
+    ];
+    var children = renderAndSlice(fullSet, 0);
+    expect(children).toEqual({
+      '[A]': fullSet[0],
+      '[B]': fullSet[1],
+      '[C]': fullSet[2]
+    });
+  });
+
+  it('should render the remaining set if no end index is supplied', function() {
+    var fullSet = [
+      <div key="A" />,
+      <div key="B" />,
+      <div key="C" />
+    ];
+    var children = renderAndSlice(fullSet, 1);
+    expect(children).toEqual({
+      '[B]': fullSet[1],
+      '[C]': fullSet[2]
+    });
+  });
+
+  it('should exclude everything at or after the end index', function() {
+    var fullSet = [
+      <div key="A" />,
+      <div key="B" />,
+      <div key="C" />,
+      <div key="D" />
+    ];
+    var children = renderAndSlice(fullSet, 1, 2);
+    expect(children).toEqual({
+      '[B]': fullSet[1]
+    });
+  });
+
+  it('should allow static children to be sliced', function() {
+    var a = <div />;
+    var b = <div />;
+    var c = <div />;
+
+    var instance = <Partial start={1} end={2}>{a}{b}{c}</Partial>;
+    ReactTestUtils.renderIntoDocument(instance);
+    var rendered = reactComponentExpect(instance)
+      .expectRenderedChild()
+      .instance();
+
+    expect(rendered.props.children).toEqual({
+      '[1]': b
+    });
+  });
+
+});
diff --git a/src/utils/sliceChildren.js b/src/utils/sliceChildren.js
new file mode 100644
index 0000000..7cd01c1
--- /dev/null
+++ b/src/utils/sliceChildren.js
@@ -0,0 +1,59 @@
+/**
+ * Copyright 2013 Facebook, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ * @providesModule sliceChildren
+ */
+
+"use strict";
+
+var flattenChildren = require('flattenChildren');
+
+/**
+ * Slice children that are typically specified as `props.children`. This version
+ * of slice children ignores empty child components.
+ *
+ * @param {*} children The children set to filter.
+ * @param {number} start The first zero-based index to include in the subset.
+ * @param {?number} end The non-inclusive last index of the subset.
+ * @return {object} mirrored array with mapped children
+ */
+function sliceChildren(children, start, end) {
+  if (children == null) {
+    return children;
+  }
+
+  var slicedChildren = {};
+  var flattenedMap = flattenChildren(children);
+  var ii = 0;
+  for (var key in flattenedMap) {
+    if (!flattenedMap.hasOwnProperty(key)) {
+      continue;
+    }
+    var child = flattenedMap[key];
+    // In this version of slice children we ignore empty children.
+    if (child !== null) {
+      if (ii >= start) {
+        slicedChildren[key] = child;
+      }
+      ii++;
+      if (end != null && ii >= end) {
+        break;
+      }
+    }
+  }
+  return slicedChildren;
+}
+
+module.exports = sliceChildren;