What is the difference between elements and components in react

The difference between elements and components in react: 1. The element data structure is an ordinary object, while the component data structure is a class or pure function; 2. In JSX, elements nested by elements will have the attribute children method to pass in the component of this element.

The difference between elements and components in react:

1. React elements

React element (React element), it is the smallest basic unit in React. We can easily create a React element using JSX syntax:

const element = <div className="element">I&#39;m element</div>

React element is not a real DOM element, it is just js plain objects, so there is no way to directly call the DOM native API. The above JSX translated object probably looks like this:

{
    _context: Object,
    _owner: null,
    key: null,
    props: {
    className: 'element'，
    children: 'I'm element'
  },
    ref: null,
    type: "div"
}

Only after the rendering of this element is completed, its corresponding DOM element can be obtained through the selector. However, according to the design idea of ​​React's finite state machine, components should be expressed using states and attributes, and DOM operations should be avoided as much as possible. Even if DOM operations are to be performed, the interfaces ref and getDOMNode() provided by React should be used. . Generally, using the interface provided by React is enough to cope with scenarios that require DOM manipulation, so powerful selectors like jQuery have almost no place in React.

In addition to using JSX syntax, we can also use React.createElement() and React.cloneElement() to build React elements.

React.createElement()

JSX syntax is to use React.createElement() to build React elements. It accepts three parameters, the first parameter can be a tag name. Such as div, span, or React component. The second parameter is the attribute passed in. The third and subsequent parameters are all subcomponents of the component.

React.createElement(
    type,
    [props],
    [...children]
)

React.cloneElement()

React.cloneElement() is similar to React.createElement(), except that the first parameter it passes in is a React elements, not tag names or components. The newly added attributes will be merged into the original attributes and passed into the returned new element, and the child elements will be replaced.

React.cloneElement(
  element,
  [props],
  [...children]
)

2. React components

There are three ways to build components in React. React.createClass(), ES6 classes and stateless functions.

React.createClass()

React.createClass() is the earliest and most compatible method among the three methods. The officially designated component writing method before version 0.14.

var Greeting = React.createClass({
  render: function() {
    return <h1 id="Hello-nbsp-this-props-name">Hello, {this.props.name}</h1>;
  }
});

ES6 class

ES6 class is currently the officially recommended way to use it. It uses ES6 standard syntax to build, but its implementation still calls React.createClass() is implemented. The life cycle and automatic binding method of ES6 class are slightly different from React.createClass().

class Greeting extemds React.Component{
  render: function() {
    return <h1 id="Hello-nbsp-this-props-name">Hello, {this.props.name}</h1>;
  }
};

Stateless function

Stateless function is a stateless component built using functions. The stateless component passes in two parameters: props and context. It has no state. Except render(), there are no other life cycle methods.

function Greeting (props) {
  return <h1 id="Hello-nbsp-props-name">Hello, {props.name}</h1>;
}

The data structure of the component built by React.createClass() and ES6 class is a class, and the data structure of the stateless component is a function. They are considered the same in React.

3. The difference between elements and components

Components are composed of elements. Element data structures are ordinary objects, while component data structures are classes or pure functions. In addition, there are a few differences to note:

this.props.children

In JSX, elements nested by elements will have the attribute children The component of this element is passed in. When only one element is nested, children is a React element, and when multiple elements are nested, children is an array of React elements. You can write children directly into JSX, but if you want to pass new attributes to them, you need to use React.cloneElement() to build new elements. I once let go of the following error:

render () {
  var Child = this.props.children
  return <div><Child tip={&#39;error!&#39;}/><div>
}

Because Child is a React element, not a component, this way of writing is completely wrong. The correct way should be:

render () {
  var child = this.props.children
  return <div>{ React.cloneElement(child, {tip: &#39;right way!&#39;}) }<div>
}

That's it, the original Existing attributes and newly added attributes are passed to the child elements together. Using React.cloneElement() is the correct way to operate elements.

User Component

Sometimes, components can allow users to pass in custom components in the form of attributes to improve the flexibility of the component. This attribute should be passed in React elements, not React components. Using React elements allows users to pass in custom components and add properties to the components at the same time. Likewise, you can use React.cloneElement() to add more properties to a custom component, or to replace child elements.

// 推荐
<MyComponent tick={
  <UserComponent tip="Yes"/>
} />
 
// 不推荐
<MyComponent tick={ UserComponent } />

Finally

Finally, to make an inappropriate analogy, the React component is MyComponent, and the React element is<mycomponent></mycomponent>.

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