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04-components.html
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<!doctype html>
<title>04 Components - React From Zero</title>
<script src="https://unpkg.com/[email protected]/umd/react.development.js"></script>
<script src="https://unpkg.com/[email protected]/umd/react-dom.development.js"></script>
<script src="https://unpkg.com/@babel/standalone/babel.min.js"></script>
<div id="app"></div>
<script type="text/babel">
// The main selling point of React is its component system
// components are used to encapsulate elements and their behaviour
// see them as a mix of controller and view of MVC
// Here we use stand alone elements and some data
var data = "world"
var reactElement =
<div>
<h1>Hello</h1>
<h2>{data}</h2>
</div>
// Here the elements are encapsuled in a simple component function
// They have to start with a capital letter and
// return exactly ONE root element with or without nested elements (before React 16)
function MyComponent() {
var data = "world"
return (
<div>
<h1>Hello</h1>
<h2>{data}</h2>
</div>
)
}
// Since React 16.0.0, components can return an array of elements as well
// In doing so, no additional wrapper element is created
// One caveat is that, similarly to what we do when rendering an array,
// we have to add a unique key to each element in the array, also don't forget the commas
// (we'll see more on this in the next lesson)
function MyComponent() {
var data = "world"
return [
<h1 key="hello">Hello</h1>,
<h2 key="data">{data}</h2>
]
}
// Since React 16.2.0, we can use special "wrapper" components called fragments
// that behave the same (no extra wrapper element created)
// but remove the need to explicitly set keys (fragments do this under the hood) and commas
function MyComponent() {
var data = "world"
return (
<React.Fragment>
<h1>Hello</h1>
<h2>{data}</h2>
</React.Fragment>
)
}
// a component function can be used like an element
reactElement = <MyComponent/>
// this translates to a React.createElement() call
// the null indicates that no properties have been set
reactElement = React.createElement(MyComponent, null)
// for reference a react-internal <div> tag
var anotherElement = <div/>
// gets converted to
anotherElement = React.createElement("div", null)
var renderTarget = document.getElementById("app")
ReactDOM.render(reactElement, renderTarget)
</script>