JavaScript Dijkstra-Algorithm

Hi there.
I'm trying to implement the dijkstra-alorithm in Javascript.
But it doesn't work.
After creating a graph the script should show me the shortest way from a start-node to another node.
My code is in the text file below.
And this is my output:

TypeError: Cannot read properties of undefined (reading 'forEach')

I followed this tutorial:
https://medium.com/@adriennetjohnson/a-walkthrough-of-dijkstras-algorithm-in-javascript-e94b74192026

Thanks for any help.