what does "setNew interpreter error: LOW_MEMORY,MEMORY" mean?

I think you are expecting your setTimeout('pause()', 20); to delay the running of the code for 20 milliseconds.....

What you have written is basically this:

while (1) {
  digitalWrite(A4, 0);

  digitalWrite(B4, 1);
  digitalWrite(B3, 0);
 
  digitalWrite(A4, 1);
  digitalWrite(B4, 0);
 
  digitalWrite(B3, 1);
}

So it is looping forever toggling the state of the pins. It is also adding new timeouts, faster than they can be executed.

The timeout calls are a callback. This means that pause() will be called 20 milliseconds later, however the next statement digitalWrite(B4, 1); gets written straight away - it does not wait 20ms before doing that.

To achieve what you want - you will need to chain calls so that the next action occurs in a call back - not directly.

I hope this helps.