无法使用在render函数外部声明的变量

Question

why is that when we declare a object outside the render function and using it in the return of the render function of a component causes an unexpected token error . If i declare the myStyle object inside the render function the below code works correctly.

import React , { Component } from 'react';


class Test extends Component {

  var myStyle={
      backgroundColor:"red",
      width:"100px",
      height:"100px",
      margin:"0 auto",
      marginTop:"50px"
  };

  render(){
    return(
       <div style={myStyle}>

      </div>
    );
  }
}

export default Test;

Thanks

Answer 1

First, since you're using ES6 class syntax, you should use const or let to define your variables.

The best solution for you though would be to set the variable into the state of the component. So you can manipulate the state easily later and rerender the component when needed with this.setState(); .

You would do it like this:

Inside the constructor method you would do -

constructor(props){
    super(props);

    this.state = {
        myStyle: {
            backgroundColor:"red",
            width:"100px",
            height:"100px",
            margin:"0 auto",
            marginTop:"50px"
        }
    }
}

After that, you can use the ES6 spread operator to apply the CSS to whatever component you like, easily.