hard-coding

currMarg = (currMarg == 1800) ? (0) : (currMarg + 600);
contStyle.marginLeft = "-%dpx".replace("%d", curMarg);

// Upon reading what this code does, I notice some hard-coding that could be done away with

const margMultiplier = -600;
currMarg = ++currMarg % 4;
contStyle.marginLeft = "%dpx".replace("%d", curMarg * margMultiplier);

// Much better. Result is 0->1->2->3->0->... versus 0->600->1200->1800->0->...