我需要帮助理解 React 应用程序中的 TypeError 吗？

Question

I am trying to make a Kanban clone. I have the following block of code which is giving a TypeError

59 |  moveItemLeft(index1,index2) {
58 |     console.log(index1,index2)
60 |     let newArr = this.state.boards.slice();
61 |     let arrItem = newArr[index1].list[index2];
62 |     newArr[index1].list.splice(index2, 1);
63 |     newArr[(index1-1)].list.push(arrItem);
64 |     this.setState({
65 |           boards: newArr,
66 |   })

    }

The error I keep getting is

TypeError: newArr[(index1 - 1)] is undefined
moveItemLeft
C:/Users/claude/documents/codecademy/premium/reactjs/triplebyte-trello/src/BoardContainer/BoardContainer.js:61

on line 61. I can't figure out why I am getting that error, the code should work.

Can anyone help?

Answer 1

I am not getting clear scenario in your question without further lines of code. However, what I am understanding here is that the arrays are empty when line 61 is getting interpreted and it is getting value afterwards. please try placing line 61 after 63.

Answer 2

I solved the problem on line 63 I did the following:

if(index1 !== 0) newArr[(index1-1)].list.push(arrItem);

for whatever reason, the right arrow calls the moved left method which I will figure out. So if index1 == 0, it cannot be decreased any farther. The same change will be made to the moveRight function, however, it will be if(index1 !== index1.length - 1).

Thank you everyone for your help.