in a React App, JSON.Stringify shows only first ltem and a length item instead of other items

In a React App, I have an array that want to convert it to JSON and send it to the server. I do it with this:

console.log(JSON.stringify(mainArray"))

And I want to test it and I expect something like this to see:

"breakfast": {
                "1": "item 1",
                "2": "item 2"
            }

But I see only first item and a length item like this:

"breakfast": {
                "1": "item 1",
                "length": 2
            }

Also when I log the array without JSON.Stringify, I see something like this:

What's that proto ? Why I dont see my whole data in a clean way? Also in this situation, Every thing works fine if I do this:

console.lo(breakfast[0]) //prints first item
console.lo(breakfast[1]) //prints second item

First I thought its console.log's display problem, But when I send it to the server I get the same. I have just a simple array and I want to see it regularly.