Removing numbers from the middle of an array
Firstly: Don't use for...in on arrays.

Secondly, I suppose you can find the 1-boundaries, and add/subtract 4:

var left = array.indexOf(1) + 4;
var right = array.lastIndexOf(1) - 4;
for(; left &lt;= right ; left++) {
  array[left] = 0;
}


Not particularly clever, but it does the job.

(Note: lastIndexOf is widely supported in modern runtimes, but older ones may not have it)

But also take @itsbruce's advice from the comments, and consider another structure for these data.