如何在数组中使用数组变量？

Question

I have an array and I want to put same array and other array inside of the first array.

var arr=["a","b","c",arr,arr2];
var arr2=["a","b"];

var arr3=[];
arr3=arr[3]; 

When I print out arr, I can see ["a","b","c",,]

But if I print out arr3, The result is undefined.

How can I fix it?

Answer 1

You need to do this in the right order:

var arr1 = [];
var arr2 = [ "a", "b" ];


// Now arr1 and arr2 are defined so you can throw them into another array:

var arr3 = [ "a", "b", "c", arr1, arr2 ];

Answer 2

You've defined arr as part of itself - arr[3] is arr . But at the time, arr doesn't exist yet, so it comes out as undefined .