Manage React Component State with setState
State is used for properties on a component that will change, versus static properties that are passed in. This lesson introduces you to updating state through a simple text input and displaying that in the browser.
[00:00] Unlike props, which are a collection of values that are meant to be passed into our component as static value, it's not meant to be changed by our component. State represents a collection of values that is meant to be managed, as well as updated by our component.
[00:14] To get us started using state, I'm going to setup a constructor method here, and the first thing I'm going to do is, I'm going to call super. This is going to give the keyword "this" the context within our component, rather than its parent class React.Component.
[00:29] Here, we're going to set up, this.state equal to an object, I'm going to create a key called "text," I'm going to say, "This is the state text."
[00:39] To use state within our JSX, we interpolate it just like we do this.props, but this time, we're going to say, this.state, and then, the key that we're looking for, in this case, it's txt. We can see in the browser there, we get this is the state text.
[00:55] Again, this is meant to be managed and updated by our component. I'm going to create a method here called "update," that takes in an event. It's important to note this is not a part of the specification, this is just a custom method on our component.
[01:08] I'm simply going to call this.setState, we're going to pass in a new object, with a key of text, and I'm going to get a new value off of that event, I'm going to say e.target.value.
[01:21] Now to get that working, I'm going to wrap this JSX in a parent node, we only have a single node being delivered by our render method. I'm going to create an input here, and on its onchange event, I'm going to call this.update, the custom method that we created. I'm going to go ahead and bind that with a context of this.
[01:43] When we run that, we've got our default state text here, and when we type in this, this is the new text, we can see that our state is in fact being updated, and every time we call this.setState, our render method is being rerun. It's important to note here that, the call of this.setState only overwrites the values that we actually send into it.
[02:07] If I created another value in our state for cat, and its default is zero. We'll go ahead and output that right here, after the text value. I'll just say cat. Save that. We can see that in the browser, when we change our state, the value for cat and our state is not lost, only the value for text is updated.