I was actually bitten by this the other day. I needed the last element from an array, so I remembered
.pop() and used it.
const arr = ["doe", "ray", "mee"]; const last = arr.pop(); // mee, but array is now ["doe", "ray"]
This certainly worked great right away, but I didn't realize the original array had changed and it caused a problem. Instead, I had to find the non-mutating alternative:
const arr = ["doe", "ray", "mee"]; const last = arr.slice(-1); // ["mee"], arr is unchanged
Related: Array Explorer