Reduce number of decimals

[EMWPEWA]

Hi
I am a newbie, but with the ambition to only ask same question once!? (we will see about that!!)
If I want to change outcome of exchange rate to 2 or 3 decimals, I shall change something here, like row 128 (I think)?

var rateSpan = document.createElement('span');
rateSpan.innerHTML = ((this.config.layoutStyle == 'ticker' && i < (this.rates.length - 1)) ? this.rates[i].rate + ' • ' : this.rates[i].rate);
rateContainer.appendChild(rateSpan);

But none of my experiment have succeeded!
Anyone that can give me some help?