This code does the following: 1. It sets `a` equal to...

This code does the following:

1. It sets a equal to 1.
2. It calls the Math.floor() function with the argument 1.9, which rounds down to 1. It then adds the negative length of an array containing the number 123, which is -1. So b is set equal to 0.
3. It divides a by b, which results in a division by zero error since b is zero.
4. It attempts to print the value of c, but since an error occurred the program will not reach this line.

In summary, this code tries to perform a division operation between a variable (a) and an expression that evaluates to zero(b) resulting in a division by zero error.