react native chrome debugger breaks the application

Question

I have a react-native sample which works fine in simulator. But when I try to debug it in the chrome, it stops working.

I am using Navigator, first page is a greeting, which works fine. When I enable debug, the behavior is like this : Go to the first page, every thing is fine. Click on enter button to enter the app, I can see the messages from my render function in chrome, but there is no visual change Click again on the same button, give erros : many

Warning: flattenChildren(...): Encountered two children with the same key, .0:$0 . Child keys must be unique; when two children share a key, only the first child will be used.

And at the end

Exception 'shadowView (for ID 19) not found' was thrown while invoking replaceExistingNonRootView on target RCTUIManager with params ( 19, 446 )

The component that might cause the error is as follows ( it is a chess board)

var Dimensions = require('Dimensions');
var fen = require('../logic/fen');
var windowSize = Dimensions.get('window');


import React, {
    AppRegistry,
    Component,
    TouchableHighlight,
    StyleSheet,
    Text,
    View
} from 'react-native';

const Square = require('./square');
const Piece = require('./piece.component');
const CONSTANTS = require('./constants');
var squares = [];
var pieces = [];
var createRow = function(i, width) {
    for (let j = 0; j < 8; j++) {
        squares.push(<Square width={width} key={i*10+j} row = {i} column = {j} onSquareSelected = {this.squareSelected}></Square>
        );
    }
}
var createBoard = function(width) {
    for (let i = 0; i < 8; i++) {
        createRow(i, width);
    }
};

const Board = React.createClass({

    componentWillMount() {
       this.pieceWidth = this.props.width/8;
       createBoard(this.pieceWidth);
       this.createPieces();

    },
    createPieces(){
        console.log('Creating pieces');
        let pieceDefinitions =  fen.read(fen.initial);
        pieces = [];
        var key = 0;
        for(let p in pieceDefinitions){

            key = key +1 ;
            console.log('piece key is ' + key)
             pieces.push(
                    <Piece key={key} width ={this.pieceWidth} coordinate={p} color = {pieceDefinitions[p].color} 
                    role = {pieceDefinitions[p].role}>
                 </Piece>
             )
        }
        return pieces;
    },
    squareSelected(row, column) {
        console.log("Row", row, "Column", column, "selected");
    },
    getInitialState() {
        return { selectedPiece: null }
    },

    render() {
        return (
            <View style={[styles.container, {width : this.props.width ,height: this.props.width}]}>
                {squares}
                {pieces}
            </View>
        )
    }
});

const styles = StyleSheet.create({
    container: {
        marginTop : 20,
        backgroundColor: '#F5FCFF',
        flexDirection: 'row',
        flexWrap: 'wrap',
    }
})

module.exports = Board;

Answer 1

Apparently any RN code that uses let breaks completely in the Chrome debugger. There is no solution. We are screwed. I believe that the transpiler used by RN wraps each block that contains even a single let in a closure, and suddenly this is something else like _this2 , but Chrome debugger doesn't know that.