assignment for jsx in double circulation

[tageecc]

Do you want to request a feature or report a bug?
bug，maybe~

What is the current behavior?

• the code is :

import React, { Component } from 'react';

class App extends Component {

    render() {

        let res = new Array(2).fill(new Array(2));
        for(let i =0;i<2;i++){
            for(let j=0;j<2;j++){
                console.log(res[i][j]);
                res[i][j]=<div>{'i:'+i+',j:'+j}</div>;
            }
        }
        return res;
    }
}

export default App;

• and the result print on the page is:

What is the expected behavior?
it's very strange, i should not start with 0?

Which versions of React, and which browser / OS are affected by this issue? Did this work in previous versions of React?

"dependencies": {
    "react": "^16.0.0",
    "react-dom": "^16.0.0",
    "react-scripts": "1.0.17"
  }

[gaearon]

This fills the top-level array with two references to the same Array object:

let res = new Array(2).fill(new Array(2));

So in the second iteration of the loop, you override the values set during the first iteration.