函数内部的render和class in reactjs [英] Function inside render and class in reactjs

问题描述

我正在努力学习反应，我有一些不确定因素。我正在引用反应DOCS和其他一些教程，我看到函数写在渲染函数内部，也在类内部。我们应该在render函数里面做什么反应？

I'm trying to learn reactjs and i have some uncertainties. I was refering react DOCS and some other tutorials and i saw functions are written inside render function and also inside class. What things should we do inside render function in react?

第一种方式

class App extends Component {

    test(user) {

        return user.firstName;
    }

    render() {

        const user = {
            firstName: 'Harper',
            lastName: 'Perez'
        };

        return (

            <div>

                <h1>{this.test(user)}</h1>

            </div>
        )
    }
}

第二种方式

class App extends Component {

       render() {

        const user = {
            firstName: 'Harper',
            lastName: 'Perez'
        };

        function test(user) {

            return user.firstName;
        }

        return (

            <div>

                <h1>{test(user)}</h1>

            </div>

        )

    }
}

这两种方法都有效。但我想知道这样做的最佳方法是什么？最重要的是，我想知道我在渲染功能中可以做什么样的事情。

Both this methods work. But i want to know what is the best method to do this? Most importantly i want to know what kind of things i can do inside render function.

谢谢。

推荐答案

我认为这最终是你的选择，但我个人更喜欢只在渲染中放置渲染组件和/或JSX的函数（即映射到prop，有条件地加载适当组件的switch语句）基于道具等...）。如果函数背后的逻辑很重，我会将它从渲染中删除。

I think it's ultimately your choice, but I personally prefer only putting functions within render that deal exclusively with rendering components and/or JSX (i.e. mapping over a prop, switch statements that conditionally load a proper component based on a prop, etc...). If the logic behind the function is heavy, I'll leave it out of render.

这是一个例子。在你的组件中说你有一个用户道具应该显示一个用户列表。你可能有这些类型的渲染函数：

Here's an example. Say in your component you have a "users" prop that is supposed to display a list of users. You might have a render function with these types of things:

render(){
  
  // An array of user objects & a status string.
  const { users, status } = this.props;
  
  // Map users array to render your children:
  const renderUserList = () => {
    return users.map(user => {
      return <div>{ user.firstName }</div>;
    });
  };
  
  // Conditionally load a component:
  const renderStatus = () => {
    let component = '';
    switch(status){
      case 'loading':
        component = <Component1 />
        break;
      case 'error':
        component = <Component2 />
        break;
      case 'success':
        component = <Component3 />
        break;
      default:
        break;
    }
    
    return component;
  }
  
  // render() return:
  return(
    <div>
      <div className="status">
        { renderStatus() }
      </div>
      <div className="user-list">
        { renderUserList() }
      </div>
    </div>
  );
}

但是，如果你有一个需要以某种方式操纵用户数据的函数，最好把它放在渲染之外的函数中。

However, if you had a function that needed to somehow manipulate data about a user, it might be better to put that in a function outside of render.

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