React component API
In this section we will discuss the React component API. We will explain the following seven methods:
Set status:
setStateReplacement status:
replaceStateSet the properties:
setPropsReplace attributes:
replacePropsForce updates:
forceUpdateGet the DOM node:
findDOMNodeDetermine the mount status of the component:
isMounted
Set status: setState
setState(object nextState[, function callback])
Parameter description
nextStatenew state to be set, which will be the same as the currentstatemerge.callbackoptional parameters, callback function. The function will be found in thesetStateset up successfully and the component is called after re-rendering.
Merge nextState and current state and re-render the component setState is the main way to trigger UI updates in React event handlers and request callbacks.
About setState
Cannot be passed within the component this.state modify the state because it will be called setState() and then replaced.
setState() doesn’t change immediately. this.state instead, create a soon-to-be processed state . setState() it is not necessarily synchronous, and React will execute in batches to improve performance. state and DOM rendering.
setState() always triggers a component redrawing, unless in the shouldComponentUpdate() some conditional rendering logic is implemented in.
Example
React instance
classCounterextendsReact.Component{constructor(props){super(props);this.state=
{clickCount:0};this.handleClick=this.handleClick.bind(this);}handleClick()
{this.setState(function(state){return{clickCount:state.clickCount+1};});}render()
{return(<h2onClick={this.handleClick}>Click me! The number of clicks is:{this.state.clickCount}</h2>);}}
ReactDOM.render(<Counter/>,document.getElementById('example'));
In the example, the click counter is increased by 1 by clicking the H2 tab.
Replacement status: replaceState
replaceState(object nextState[, function callback])
nextStatethe new state to be set, which replaces the currentstate.callbackoptional parameters, callback function. The function will be found in thereplaceStateset up successfully and the component is called after re-rendering.
replaceState() methods and setState() similar, but the method only retains nextState in state, original state not here nextState all the states in the are deleted.
Set property: setProps
setProps(object nextProps[, function callback])
nextPropsthe new property to be set, the state will be the same as the currentpropsmergecallbackoptional parameters, callback function. The function will be found in thesetPropsset up successfully and the component is called after re-rendering.
Set the component properties and re-render the component.
props is equivalent to the data flow of a component, which is always passed down from the parent component to all child components. When integrating with an external JavaScript application, we may need to pass data or notification to the component React.render() components need tobe re-rendered, and you can use the setProps() .
Update the component so that I can call it again on the node React.render() can also be done through setProps() method to change the properties of the component and trigger the component to re-render.
Replace attributes: replaceProps
replaceProps(object nextProps[, function callback])
nextPropsthe new property to be set, which replaces the currentprops.callbackoptional parameters, callback function. The function will be found in thereplacePropsset up successfully and the component is called after re-rendering.
replaceProps() methods and setProps similar, but it deletes the original props .
Force updates: forceUpdate
forceUpdate([function callback])
Parameter description
callbackoptional parameters, callback function. This function will be used in the componentrender()called after the method is called.
forceUpdate() method causes the component to call its own render() method to re-render the component, and the component’s child components also call their own render() . However, when the component renders again, it still reads the this.props and this.state if the state does notchange, React will only update the DOM
forceUpdate() method is applicable to this.props and this.state redraw components other than (e. G. modified this.state . This method notifies React that it needs to call render()
Generally speaking, you should try to avoid using forceUpdate() and only from this.props and this.state read the status in and triggered by React render() call.
Get DOM node: findDOMNode
DOMElement findDOMNode()
Return value: DOM element
DOMElement
If the component is already mounted in DOM, the method returns the corresponding local browser DOM element. When render return null or false hour this.findDOMNode() will also return null . Thismethod is useful when reading values from DOM, such as getting the value ofa form field and doing some DOM operations.
Determine the mount status of the component: isMounted
bool isMounted()
Return value:
trueorfalseindicating whether the component has been mounted into the DOM
isMounted() method is used to determine whether the component has been mounted into the DOM. You can use this method to ensure setState() and forceUpdate() calls in asynchronous scenarios do not go wrong.
This article refers to: http://itbilu.com/javascript/react/EkACBdqKe.html