Although HA is available in TradingView by default, this script is to recalculate HA by traditional calculations.
This version REPAINTS!! This is because Traditional HA uses Close Price (which is calculated on the fly).
In true TradingView spirit, the author of this script has published it open-source, so traders can understand and verify it. Cheers to the author! You may use it for free, but reuse of this code in a publication is governed by House Rules. You can favorite it to use it on a chart.