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Learn how to make a child component update its parent.

Child Components Update Their Parents' state

In the last exercise, you defined a function in `Parent` that can change `Parent`'s state.

`Parent` must pass this function down to `Child`, so that `Child` can use it in an event listener on the dropdown menu.

Pass the Event Handler

To make a child component update its parent's `state`, the first step is something that you've seen before:  you must define a state-changing method on the parent.

Define an Event Handler

You just passed a function down to `Child` that can change `Parent`'s state! 

Receive the Event Handler

How does a stateless, child component *update* the state of the parent component? Here's how that works:

*1*

The *parent* component class defines a method that calls `this.setState()`.

For an example, look in **Step1.js** at the `.handleClick()` method.

*2*

The parent component binds the newly-defined method to the current instance of the component in its constructor. This ensures that when we pass the method to the child component, it will still update the parent component.

For an example, look in **Step2.js** at the end of the `constructor()` method.

*3*

Once the *parent* has defined a method that updates its state and bound to it, the parent then passes that method down to a *child.*

Look in **Step2.js**, at the `prop` on line 28.

*4*

The *child* receives the passed-down function, and uses it as an event handler.

Look in **Step3.js**.  When a user clicks on the `<button></button>`, a click event will fire.  This will make the passed-down function get called, which will *update* the parent's state.

Great work!  *Stateless components updating their parents' state* is a React pattern that you'll see more and more.  Learning to recognize it will help you understand how React apps are organized.

Click Next to move on to the final version of our programming pattern! 