fix: remove empty class attribute left behind after htmx operations

After htmx removes its utility classes (swapping, settling, request),
elements are left with an empty class="" attribute if they had no other
classes. This happens because doSettle and the request indicator cleanup
use raw classList.remove instead of removeClassFromElement, which
already handles empty class attribute removal.

Replace classList.remove with removeClassFromElement at three sites:
- swappingClass removal (line 1978)
- settlingClass removal in doSettle (line 1999)
- requestClass removal from indicators (line 3415)

Fixes #1701
Supersedes #2683

Author: manwithacat

src/htmx.js

@@ -1975,7 +1975,7 @@ var htmx = (function() {
         }
       }
 
-      target.classList.remove(htmx.config.swappingClass)
+      removeClassFromElement(target, htmx.config.swappingClass)
       forEach(settleInfo.elts, function(elt) {
         if (elt.classList) {
           elt.classList.add(htmx.config.settlingClass)
@@ -1996,7 +1996,7 @@ var htmx = (function() {
         })
         forEach(settleInfo.elts, function(elt) {
           if (elt.classList) {
-            elt.classList.remove(htmx.config.settlingClass)
+            removeClassFromElement(elt, htmx.config.settlingClass)
           }
           triggerEvent(elt, 'htmx:afterSettle', swapOptions.eventInfo)
         })
@@ -3412,7 +3412,7 @@ var htmx = (function() {
     forEach(indicators, function(ic) {
       const internalData = getInternalData(ic)
       if (internalData.requestCount === 0) {
-        ic.classList.remove.call(ic.classList, htmx.config.requestClass)
+        removeClassFromElement(ic, htmx.config.requestClass)
       }
     })
     forEach(disabled, function(disabledElement) {

test/core/class-cleanup.js

@@ -0,0 +1,71 @@
+describe('Class attribute cleanup after htmx operations', function() {
+  beforeEach(function() {
+    this.server = makeServer()
+    clearWorkArea()
+  })
+  afterEach(function() {
+    this.server.restore()
+    clearWorkArea()
+  })
+
+  it('removes empty class attribute after settling class is removed', function() {
+    this.server.respondWith('GET', '/test', 'Settled!')
+
+    var div = make('<div hx-get="/test">Click Me!</div>')
+    // Element starts with no class attribute
+    should.not.exist(div.getAttribute('class'))
+
+    div.click()
+    this.server.respond()
+
+    div.innerHTML.should.equal('Settled!')
+    // After settle, the settling class should be gone and no empty class="" left behind
+    should.not.exist(div.getAttribute('class'))
+  })
+
+  it('removes empty class attribute after swapping class is removed', function() {
+    this.server.respondWith('GET', '/test', '<div id="target">Swapped!</div>')
+
+    var div = make('<div id="target" hx-get="/test" hx-swap="outerHTML">Click Me!</div>')
+    should.not.exist(div.getAttribute('class'))
+
+    div.click()
+    this.server.respond()
+
+    var result = byId('target')
+    result.innerHTML.should.equal('Swapped!')
+    should.not.exist(result.getAttribute('class'))
+  })
+
+  it('preserves existing classes and only removes htmx utility classes', function() {
+    this.server.respondWith('GET', '/test', 'Done!')
+
+    var div = make('<div class="my-class" hx-get="/test">Click Me!</div>')
+    div.getAttribute('class').should.equal('my-class')
+
+    div.click()
+    this.server.respond()
+
+    div.innerHTML.should.equal('Done!')
+    // Original class should remain, htmx utility classes should not
+    div.getAttribute('class').should.equal('my-class')
+  })
+
+  it('removes empty class attribute from indicators after request completes', function() {
+    this.server.respondWith('GET', '/test', 'Done!')
+
+    var indicator = make('<div id="ind"></div>')
+    var btn = make('<button hx-get="/test" hx-indicator="#ind">Click Me!</button>')
+
+    should.not.exist(indicator.getAttribute('class'))
+
+    btn.click()
+    // During request, indicator should have the request class
+    indicator.classList.contains(htmx.config.requestClass).should.equal(true)
+
+    this.server.respond()
+
+    // After request, indicator should not have an empty class attribute
+    should.not.exist(indicator.getAttribute('class'))
+  })
+})