为什么我会收到Uncaught TypeError：无法在分配时读取未定义的属性“ 0”？

Question

I have:

var lineItemTracker = new Array();
lineItemsTracker[i]['sales_order_line_item_id'] = result[i].sales_order_line_item_id;

This throws the error

Uncaught TypeError: Cannot read property '0' of undefined on assign

if I check

console.log(result[i].sales_order_line_item_id);

then I get the correct result. When I check

console.log('here ' + lineItemsTracker[i]['sales_order_line_item_id']);

I get the error message.

lineItemsTracker[1]['sales_order_line_item_id'] = 'test';

Produces the error. Is there a workaround?

Answer 1

Edit: As noted by others, you have a typo, but even After correcting the typo it will not work with the code you have written.

You are trying to access an invalid index and as a result you are getting the error. Use the push method of the Array to add the elements.

var lineItemTracker = new Array();
lineItemsTracker.push(result[i].sales_order_line_item_id);

Explaination:

1. When you create an array like var lineItemTracker = new Array(); lineItemTracker is created an an array but the length is 0 .

2. Next, when you write lineItemsTracker[i] it means you are trying to access the element at index i . Since, the length of the array is zero, It will return undefined as there is no element defined at that index.

3. Next, lineItemsTracker[i]['sales_order_line_item_id'] This lines try to access the property sales_order_line_item_id on an undefined object and then you will get the error.

Uncaught TypeError: Cannot read property 'sales_order_line_item_id' of undefined on assign

Answer 2

You have a typo. It should be var lineItemsTracker = new Array();

You don't have an s in the definition but you put an s everywhere you reference it