Detailed knowledge of react

　　用react一年多了.一直是在别人的影子下写的代码,他们也确实都是大神级的人物,不过,小菜鸟也有小菜鸟的思想~这不,今天就在重温一遍react!记一些零碎的知识点~所有的这些均参考于  

　　react官方文档 facebook.github.io/react/docs/events.html#supported-events

　　1　　var names = ['fr','de']

　　　ReactDOM.render(

　　　　(1)

你好,学长

　　　　document.getElementById('h1')

 

　　　　(2)

　　　　　　{

　　　　　　　　names.map(function(name){

　　　　　　　　　　return

Hello {name}

　　　　　　　　})

　　　　　　}

　　　　　

　document.getElementById('h1')　

　 )

ReactDom.render is the basic syntax of React. Use: Convert template to HTML and insert the specified DOM Node

The unique syntax of react: JSX The above example allows mixed writing of HTML and JavaScript

The basic syntax rules of JSX: 1 When an HTML tag starts with <>, it will be parsed using HTML rules , when a code block starts with {}, it will be parsed by javaScript

Component: React allows the code to be encapsulated into a component, and then insert this component into the web page just like inserting an ordinary HTML tag. React.createClass is used to Generate a component class, and the component class can only have one top-level tag

This is wrong because it has two tags and should contain a

tag at the outermost part

The usage of components is consistent with the usage of HTML tags. The properties of components can be obtained using this.props object. One thing to note: its class and for attributes need to be changed to className and htmlFor, because class and for are reserved words in JavaScript

The properties of this.props correspond to the properties of the component one-to-one, but this.props.children represents all the child nodes of the component. This.props.children has three possibilities. If there are no child nodes, it means undefind, and there are A child node represents an object, and if there are multiple child nodes, it is an array. React provides a tool method to handle this.props.children, which is React.Children.map() to traverse the child nodes

　PropTypes Properties: Verify whether the properties of the component instance meet the requirements. propTypes is a configuration object used to define property types, such as:

Obtain the real DOM Node: Use this.refs.[refName]

This.state and this.props both describe the characteristics of the component. The difference is: this.state refers to the characteristics that can be changed, while this.props refers to the characteristics that can be changed. It is a feature that cannot be changed once defined

React life cycle:

　-[] The life cycle of a React component is divided into three parts: 1 Inserted real DOM:Mounting(instantiation ), 2 Updating: Being re-rendered (existence period) 3 The real DOm has been removed (destroy & cleanup period), the following is the specific order

##　　　-[Note]componentDidMount Will not be called while the server is being rendered.

　　-[Solution] Detailed description of each cycle:

　　　getDefaultProps

　　　For each component instance, this method will only be called once. In all subsequent applications of the component class, getDefaultPops will no longer be called, and the object returned can be used to set the default props (abbreviation for properties) values.

　　　　getInitialState

　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　   forward through call to each instance of the component, this method can be called

only once, is used to initialize each instance. state, in this method, you can access the component's props. Each React component has its own state, which differs from props in that state only exists inside the component, while props are shared among all instances.

There is a difference between the calls of getInitialState and getDefaultPops. getDefaultPops is only called once for the component class, and subsequent applications of this class will not be called, while getInitialState is called for each component instance. , and only adjust it once.

Every time the state is modified, the component will be re-rendered. After instantiation, the component will be updated through the state, and the following methods will be called in sequence:

1, shouldComponentUpdate

2, componentWillUpdate
3, render
4, componentDidUpdate

But

Do not modify this.state directly, but through the this.setState method.

##　　　ComponentWillMount

This method is called before the first rendering and is also the last chance to modify the state before the render method is called.

　　　　render

　　　This method will create a virtual DOM to represent the output of the component. For a component, the render method is the only required method. The render method needs to meet the following points:

The data can only be accessed through this.props and this.state (cannot be modified)
can return null, false or any React component
Only one top-level component can appear and cannot return a set of elements
Cannot change the state of the component
Cannot modify the output of DOM
The result returned by the render method is not a real DOM element, but a virtual representation, similar to a DOM The object of the tree structure. This is the reason why react is so efficient.

　　　ComponentDidMount

　　　　This method will not be called during the process of the server being rendered. When this method is called, the real DOM has been rendered. You can access the real DOM through this.getDOMNode() in this method (it is recommended to use ReactDOM.findDOMNode()) . Because components are not real DOM nodes, but a data structure that exists in memory, called virtual DOM. Only when it is inserted into the document will it become a real DOM. Sometimes you need to get the real DOM node from the component, then you need to use the ref attribute: such as:

　　　ComponentWillReceiveProps

　　Component The props property can be changed by the parent component, at which time componentWillReceiveProps will be called in the future. You can update the state in this method to trigger the render method to re-render the component.

ShouldComponentUpdate

If you are sure that changes in the component's props or state do not require re-rendering, you can return false in this method. Prevent the re-rendering of the component. Returning `false will not execute the render and subsequent componentWillUpdate and componentDidUpdate methods.

This method is optional and is not used in development in most cases.

　　　ComponentWillUpdate

This method is similar to componentWillMount. When the component receives new props or state is about to be re-rendered, componentWillUpdate(object nextProps, object nextState) will be called Call, Be careful not to update props or state in this aspect.

##　　　　componentDidUpdate

　　　　　　　　　　　　　　　　　　　　　　　　　　 　　　　This method is similar to componentDidMount. After the component is re-rendered, componentDidUpdate(object prevProps, object prevState) will be called. The DOM can be accessed and modified here.

　　　ComponentWillUnmount

Whenever React finishes using a component, the component must be unloaded from the DOM and then destroyed. At this time, componentWillUnmout will be executed to complete all cleanup and To destroy work, tasks added in componentDidMount need to be undone in this method, such as created timers or event listeners.

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