merge value attribute as long as the property matches (#3058)

We exclude the value from being merged on focused inputs, because the
user's input should always win.
We can still assign it as long as the value property is the same, though.
This prevents a situation where the updated hook is not being triggered
when an input is back in its "original state", because the attribute
was never changed.

Fixes #2163.

assets/js/phoenix_live_view/dom.js

@@ -405,6 +405,18 @@ let DOM = {
         if(target.getAttribute(name) !== sourceValue && (!isIgnored || (isIgnored && name.startsWith("data-")))){
           target.setAttribute(name, sourceValue)
         }
+      } else {
+        // We exclude the value from being merged on focused inputs, because the
+        // user's input should always win.
+        // We can still assign it as long as the value property is the same, though.
+        // This prevents a situation where the updated hook is not being triggered
+        // when an input is back in its "original state", because the attribute
+        // was never changed, see:
+        // https://github.com/phoenixframework/phoenix_live_view/issues/2163
+        if(name === "value" && target.value === source.value){
+          // actually set the value attribute to sync it with the value property
+          target.setAttribute("value", source.getAttribute(name))
+        }
       }
     }