forEach failure at undefined array

Question

For a very long time I used

for (var n in nodes) {f(nodes[n])} 

quite successfully. But, switching to the neat

nodes.forEach(f)

I have noticed that it fails at undefined nodes, whareas for-in loop did not. I wonder, how can I make forEach to operate identically?

Answer 1

Well, you can't. Because .forEach is just a function, and you can't call a function on null/undefined. What you could do is:

(arr || []).forEach(f);

But for these cases I recommend to use the for of loop or the regular for loop, which are both identical to .forEach. for in has a different semantic.