How to efficiently detect if anyof several fields changed?

Here's a bit I'm maintaining in the D&D_OED character sheet script, to add up encumbrance values. There are 40 text fields titled attr_enc_1 , etc.     // Gather encumbrance fields     const items = [];     for ( i = 1; i <= 40; i++ ) {         items.push( 'enc_' + i );     }     // Compute total encumbrance     items.forEach( item => {         on( `change:${item} sheet:opened`, () => {             var total = 0;             getAttrs( items, values => {                 items.forEach( enc => {                     total += (parseFloat( values[enc] ) || 0);                 });                 setAttrs({total_enc: total});             });         });     }); The thing I notice here is a particular inefficiency: on sheet:opened, it seems that this script will re-compute the total encumbrance 40 times over (once for each item in the array, due to the outer forEach loop; i.e., 1600 total additions). Right? I can detect a bit of a hiccup-delay when the sheet loads as a result. I've tried a few things (e.g., an initial scan and setting a "needToRecompute" variable then an if statement), but nothing I'm trying seems to work. What the best way to make this efficient, and just compute the total once any time either sheet:opened or any change:enc_X occurs?

For something like this, you don't want to replicate the sheet:opened  listener in each piece of the forEach; that should be it's own thing outside of the forEach. If you really need to do this on sheet open, the easy way to do it is to functionalize your on listener like so: // Gather encumbrance fields const items = []; for ( i = 1; i <= 40; i++ ) { items.push( 'enc_' + i ); } const computeEncumbrance = () => { getAttrs( items, values => { var total = 0; items.forEach( enc => { total += (parseFloat( values[enc] ) || 0); }); setAttrs({total_enc: total}); }); }; // Compute total encumbrance on('sheet:opened',computeEncumbrance); items.forEach( item => { on( `change:${item}`, computeEncumbrance); }); However, I'd wonder why you need to do this on sheet open. The encumbrance can't change without triggering the listener, so there's no situation where this should not already be computed at startup. If you're doing this to cover for crashes in the sheet, the better option is to find what's causing those crashes and fix that.

Scott C. said: For something like this, you don't want to replicate the sheet:opened  listener... This sounds solid to me. I've removed the sheet:opened listener from that point and others in the script (and added some reasonable starting defaults in the HTML), and it seems to be working fine, and much snappier to open. Thanks for the insight.

sheet:opened is very useful when you are creating and testing workers, but generally speaking, you shouldn't use it in live code unless you have a specific reason to do so. I'm sure Scott was chafing at the bit fpr not pointing this out, but you also have getAttrs and setAttrs inside a loop, which is generally a bad idea. It will work, but it can be very slow and cause lag. Each run of computeEncumbrancedoes this, so you will be doing it for every item in items. It would be better to rewrite this so you only have one getAttrs (which includes all the items), a worker body that calculates everything in items, and a single setAttrs which saves all the calculated attributes.

Eh, in this case, it's not a bad thing. The function is run as the listener, so it's only ever run once for a given event. I would not however recommend calling this function from other functions. That way lies much lag.

Thanks for considering that aspect. I'll confess I had to think about the same thing for a minute, but with the sheet:opened removed from the listener, it seems to pass the smell test (loop body only happens once per event) on my end. Ironically, one place I added a sheet:opened listener today was to create a hidden attribute on the sheet, esp. the first time the sheet is actually created. I don't know if there's otherwise a best practice in how to do that?

You can simply use a type hidden input: <input type="hidden" name="attr_hidden_attribute" value=""> It'll still show up on the attributes and abilities tab, but the only way to avoid that is to make a repeating attribute.

Great, much better, thanks for that!