Add skipinit modifier

CHANGELOG.md

@@ -9,6 +9,7 @@ Each tagged version of Datastar is accompanied by a release note. Read the [rele
 ### Added
 
 - Added the ability for checkbox input elements to set bound signals to an array of values by predefining the signal as an array ([#664](https://github.com/starfederation/datastar/issues/674)).
+- Added the `__skipinit` modifier to the `data-on-signals-change` attribute that prevents the expression being called when the attribute is first applied ([#682](https://github.com/starfederation/datastar/issues/682)).
 
 ### Changed
 
@@ -19,5 +20,4 @@ Each tagged version of Datastar is accompanied by a release note. Read the [rele
 ### Fixed
 
 - Fixed a bug in which `datastar-remove-fragments` events were not having any effect ([#664](https://github.com/starfederation/datastar/issues/664)).
-- Fixed a bug in which `datastarNaN` could be used as an auto-generated element ID ([#679](https://github.com/starfederation/datastar/issues/679)).
-- Fixed a bug in which the expression passed into `data-on-signals-change` was being called each time the attribute was evaluated ([#682](https://github.com/starfederation/datastar/issues/682)).
+- Fixed a bug in which `datastarNaN` could be used as an auto-generated element ID ([#679](https://github.com/starfederation/datastar/issues/679)).

library/src/plugins/official/dom/attributes/on.ts

@@ -121,6 +121,10 @@ export const On: AttributePlugin = {
 
     if (key.startsWith(SIGNALS_CHANGE_PREFIX)) {
       if (key === SIGNALS_CHANGE_PREFIX) {
+        const skipinit = mods.has('skipinit')
+        if (!skipinit) {
+          callback()
+        }
         const signalFn = (event: CustomEvent<DatastarSignalEvent>) =>
           callback(event)
         document.addEventListener(DATASTAR_SIGNAL_EVENT, signalFn)