docs tips parent-child communication 2

docs/_data/nav_tips.yml

@@ -28,3 +28,5 @@
     title: False in JSX
   - id: communicate-between-components
     title: Communicate Between Components
+  - id: expose-component-functions
+    title: Expose Component Functions

docs/tips/14-communicate-between-components.md

@@ -4,6 +4,7 @@ title: Communicate Between Components
 layout: tips
 permalink: communicate-between-components.html
 prev: false-in-jsx.html
+next: expose-component-functions.html
 ---
 
 For parent-child communication, simply [pass props](/react/docs/multiple-components.html).

docs/tips/15-communicate-between-components-2.md

@@ -0,0 +1,59 @@
+---
+id: expose-component-functions
+title: Expose Component Functions
+layout: tips
+permalink: expose-component-functions.html
+prev: communicate-between-components.html
+---
+
+There's another (uncommon) way of [communicating between components](/react/tips/communicate-between-components.html): simply expose a method on the child component for the parent to call.
+
+Say a list of todos, which upon clicking get removed. If there's only one unfinished todo left, animate it:
+
+```js
+/** @jsx React.DOM */
+
+var Todo = React.createClass({
+  render: function() {
+    return <div onClick={this.props.onClick}>{this.props.title}</div>;
+  },
+
+  //this component will be accessed by the parent through the `ref` attribute
+  animate: function() {
+    console.log('Pretend %s is animating', this.props.title);
+  }
+});
+
+var Todos = React.createClass({
+  getInitialState: function() {
+    return {items: ['Apple', 'Banana', 'Cranberry']};
+  },
+
+  handleClick: function(i) {
+    var items = this.state.items;
+    items.splice(i, 1);
+    this.setState({items: items}, function() {
+      if (items.length === 1) {
+        this.refs.item0.animate();
+      }
+    }.bind(this));
+  },
+
+  render: function() {
+    return (
+      <div>
+        {this.state.items.map(function(item, i) {
+          var boundClick = this.handleClick.bind(this, i);
+          return (
+            <Todo onClick={boundClick} key={i} title={item} ref={'item' + i} />
+          );
+        }, this)}
+      </div>
+    );
+  }
+});
+
+React.renderComponent(<Todos />, mountNode);
+```
+
+Alternatively, you could have achieve this by passing the `todo` an `isLastUnfinishedItem` prop, let it check this prop in `componentDidUpdate`, then animate itself; however, this quickly gets messy if you pass around different props to control animations.