How to read out the inner array length of a 2 dimensional array in javascript

I need to detect the length of an inner array within a 2d array in my application. But unfortunately it always raises a “TypeError: Cannot read property ‘length’ of undefined” error. Does anyone detect an error? Thanks a bunch

This is the 2d array called currentNodeData (console.log(currentNodeData)):

enter image description here

And this is how I want to receive the length of the inner array, which should be 6:


And this is the error:

enter image description here