From 8b59cb93836bfd13b9d38a245c64374baa489722 Mon Sep 17 00:00:00 2001
From: Carson Gross <carson@bigsky.software>
Date: Fri, 5 Jan 2024 13:11:30 -0700
Subject: [PATCH] docs + config of head handling

---
 src/htmx.js                       | 36 ++++++++++++-----------
 test/index.html                   |  2 +-
 www/content/attributes/hx-swap.md |  9 ++++++
 www/content/docs.md               | 48 ++++++++++++++++++++++++++++---
 4 files changed, 74 insertions(+), 21 deletions(-)

diff --git a/src/htmx.js b/src/htmx.js
index 4ecd9298..9794df4c 100644
--- a/src/htmx.js
+++ b/src/htmx.js
@@ -61,7 +61,7 @@ var htmx = (function() {
       disableInheritance: false,
       head : {
         boost : "merge",
-        other: "title",
+        other: "none",
       },
       responseHandling: [
         { code: '204', swap: false },
@@ -1143,17 +1143,12 @@ var htmx = (function() {
     }
   }
 
-  function handleHeadTag(head, defaultStrategy) {
-
-    if (head && htmx.config.head) {
-
-      if (defaultStrategy === "none") {
-        return
-      }
+  function handleHeadTag(head, strategy) {
 
+    if (head && (strategy === "merge" || strategy === "append")) {
       // allow new head to override merge strategy
-      let elementMergeStrategy = getAttributeValue(head, "hx-head") || defaultStrategy;
-      if (elementMergeStrategy === "append" || elementMergeStrategy === "merge") {
+      let elementMergeStrategy = getAttributeValue(head, "hx-head") || strategy;
+      if (elementMergeStrategy === "merge" || elementMergeStrategy === "append") {
         let removed = []
         let appended = []
 
@@ -2216,7 +2211,7 @@ var htmx = (function() {
         const historyElement = getHistoryElement()
         const settleInfo = makeSettleInfo(historyElement)
         handleTitle(fragment.title);
-        handleHeadTag(fragment.head, "merge");
+        handleHeadTag(fragment.head, htmx.config.head.boost);
 
         // @ts-ignore
         swapInnerHTML(historyElement, content, settleInfo)
@@ -2239,7 +2234,7 @@ var htmx = (function() {
       const historyElement = getHistoryElement()
       const settleInfo = makeSettleInfo(historyElement)
       handleTitle(fragment.title);
-      handleHeadTag(fragment.head, "merge");
+      handleHeadTag(fragment.head, htmx.config.head.boost);
       swapInnerHTML(historyElement, fragment, settleInfo)
       settleImmediately(settleInfo.tasks);
       setTimeout(function() {
@@ -2586,6 +2581,8 @@ var htmx = (function() {
             swapSpec.transition = value.substr(11) === 'true'
           } else if (value.indexOf('ignoreTitle:') === 0) {
             swapSpec.ignoreTitle = value.substr(12) === 'true'
+          } else if (value.indexOf('head:') === 0) {
+            swapSpec.head = value.substr(5)
           } else if (value.indexOf('scroll:') === 0) {
             const scrollSpec = value.substr(7)
             var splitSpec = scrollSpec.split(':')
@@ -3381,6 +3378,7 @@ var htmx = (function() {
     const shouldSwap = responseHandling.swap
     let isError = !!responseHandling.error
     let ignoreTitle = htmx.config.ignoreTitle || responseHandling.ignoreTitle
+    let head = responseInfo.boosted ? htmx.config.head.boost : htmx.config.head.other
     let selectOverride = responseHandling.select
     if (responseHandling.target) {
       responseInfo.target = querySelectorExt(elt, responseHandling.target)
@@ -3408,7 +3406,8 @@ var htmx = (function() {
       serverResponse,
       isError,
       ignoreTitle,
-      selectOverride
+      selectOverride,
+      head
     }, responseInfo)
 
     if (responseHandling.event && !triggerEvent(target, responseHandling.event, beforeSwapDetails)) return
@@ -3419,6 +3418,7 @@ var htmx = (function() {
     serverResponse = beforeSwapDetails.serverResponse // allow updating content
     isError = beforeSwapDetails.isError // allow updating error
     ignoreTitle = beforeSwapDetails.ignoreTitle // allow updating ignoring title
+    head = beforeSwapDetails.head // allow updating head algorithm
     selectOverride = beforeSwapDetails.selectOverride // allow updating select override
 
     responseInfo.target = target // Make updated target available to response events
@@ -3447,6 +3447,9 @@ var htmx = (function() {
       if (swapSpec.hasOwnProperty('ignoreTitle')) {
         ignoreTitle = swapSpec.ignoreTitle
       }
+      if (swapSpec.hasOwnProperty('head')) {
+        head = swapSpec.head
+      }
 
       target.classList.add(htmx.config.swappingClass)
 
@@ -3524,10 +3527,10 @@ var htmx = (function() {
             handleTitle(settleInfo.title);
           }
 
+          console.log("Here", head)
           // merge in new head after swap but before settle
           if (triggerEvent(document.body, "htmx:beforeHeadMerge", {head: settleInfo.head})) {
-            handleHeadTag(settleInfo.head, responseInfo.boosted ? htmx.config.head.boost :
-                htmx.config.head.other);
+            handleHeadTag(settleInfo.head, head);
           }
 
           if (hasHeader(xhr, /HX-Trigger-After-Swap:/i)) {
@@ -3642,8 +3645,9 @@ var htmx = (function() {
  * @param {import("./htmx").HtmxExtension} extension
  */
   function defineExtension(name, extension) {
+    if (name === "head-support") return; // ignore the head support extension, now integrated into htmx
     if (extension.init) {
-      extension.init(internalAPI)
+      extension.init(internalAPI);
     }
     extensions[name] = mergeObjects(extensionBase(), extension)
   }
diff --git a/test/index.html b/test/index.html
index d512a2ea..6722c52f 100644
--- a/test/index.html
+++ b/test/index.html
@@ -9,7 +9,7 @@
     <meta http-equiv="expires" content="0" />
     <meta http-equiv="expires" content="Tue, 01 Jan 1980 1:00:00 GMT" />
     <meta http-equiv="pragma" content="no-cache" />
-    <meta name="htmx-config" content='{"historyEnabled":false,"defaultSettleDelay":0,"head":false}'>
+    <meta name="htmx-config" content='{"historyEnabled":false,"defaultSettleDelay":0,"head":{"boost":"none","other":"none"}}'>
 </head>
 <body style="padding:20px;font-family: sans-serif">
 
diff --git a/www/content/attributes/hx-swap.md b/www/content/attributes/hx-swap.md
index f4ef401a..c0a04b6c 100644
--- a/www/content/attributes/hx-swap.md
+++ b/www/content/attributes/hx-swap.md
@@ -39,6 +39,15 @@ If you want to use the new [View Transitions](https://developer.mozilla.org/en-U
 when a swap occurs, you can use the `transition:true` option for your swap.  You can also enable this feature globally by
 setting the `htmx.config.globalViewTransitions` config setting to `true`.
 
+#### `head` tag handling: `head`
+
+If you want to modify how a `head` tag found in the new content is handled, you can use the `head` modifier, with one
+of the following values:
+
+* `merge` - merge the new head tag elements into the existing element
+* `append` - append the new head tag elements to the existing head tag
+* `none` - ignore any new head tag elements
+
 #### Timing: `swap` & `settle`
 
 You can modify the amount of time that htmx will wait after receiving a response to swap the content
diff --git a/www/content/docs.md b/www/content/docs.md
index bad4ddc0..e14a6cda 100644
--- a/www/content/docs.md
+++ b/www/content/docs.md
@@ -29,6 +29,7 @@ custom_classes = "wide-content"
   * [confirming](#confirming)
 * [inheritance](#inheritance)
 * [boosting](#boosting)
+  * [head tag handling](#head)
 * [websockets & SSE](#websockets-and-sse)
 * [history](#history)
 * [requests & responses](#requests)
@@ -182,10 +183,6 @@ To upgrade to htmx 2.0 from htmx 1.0, you will need to do the following:
     `htmx.config.methodsThatUseUrlParams` to `["get"]` (it's a little crazy, but `DELETE`, according to the spec, should
      use request parameters.)
   * If you want to make cross-domain requests with htmx, revert `htmx.config.selfRequestsOnly` to `false`
-  * If you want to revert these to the htmx 1.x defaults, you can use the following meta tag:
-  ```html
-  <meta name="htmx-config" content='{"scrollBehavior":"smooth", "methodsThatUseUrlParams":["get"], "selfRequestsOnly": false}'>
-  ```
 * Convert any `hx-on` attributes to their `hx-on:` equivalent:
   ```html
      <button hx-get="/info" hx-on="htmx:beforeRequest: alert('Making a request!')
@@ -202,6 +199,9 @@ To upgrade to htmx 2.0 from htmx 1.0, you will need to do the following:
   Note that you must use the kebab-case of the event name due to the fact that attributes are case-insensitive in HTML.
   ```
 * The `htmx.makeFragment()` method now **always** returns a `DocumentFragment` rather than either an `Element` or `DocumentFragment`
+* If you are using htmx in a module setting, we now provide module-type specific files for all three of the major 
+  JavaScript module types: `/dist/htmx.esm.js`, `/dist/htmx.umd.js` & `/dist/htmx.amd.js`
+* htmx 2.0 offers [automatic head merging](#head-support) with boosted links.  If you do not want this behavior, set you can set `htmx.config.head.boosted` to `"none"`
 
 IE is no longer supported in htmx 2.0, but htmx 1.x continues to support IE and will be supported for the foreseeable 
 future.
@@ -779,6 +779,46 @@ Here is an example:
 
 The anchor tag in this div will issue an AJAX `GET` request to `/blog` and swap the response into the `body` tag.
 
+### `head` tag support
+
+In boosted requests, if a head tag is detected in the response, htmx will automatically synchronize the content of
+the current head tag with the new content.  This means that elements that are already found in the current head will
+be left alone (and, therefore, not trigger another request), but new elements found in the new header will be added
+to the existing header tag.  Elements that are not found in the new head will be removed from the existing head tag.
+
+This allows you to include page-specific header related elements and have them added or removed via boosted requests.
+
+htmx also supports an "append" mode, that will simply append the content of the new head tag to the current head, if
+ the new content is not already in it.  You can control the mode that htmx will use with the `hx-head` attribute on
+the head tag in the *new* content:
+
+* `merge` - follow the merging algorithm outlined above
+* `append` - append elements that do not exist in it to the existing head, but don't remove any elements
+
+#### Controlling Merge Behavior Per Element
+
+You may also control merging behavior of individual elements with the following attributes:
+
+* If you place `hx-head="re-eval"` on a head element, it will be re-added (removed and appended) to the head tag on every
+  request, even if it already exists.  This can be useful to execute a script on every htmx request, for example.
+* If you place `hx-preserve="true"` on an element, it will never be removed from the head, regardless
+
+#### Configuring Boost & Non-Boost `head` behavior
+
+You can configure the default head behavior by setting the `boost` and `other` attributes in the `htmx.config.head` object,
+using the following values:
+
+* `merge` - merge the new head tag elements into the existing element
+* `append` - append the new head tag elements to the existing head tag
+* `none` - ignore any new head tag elements
+
+By default, `htmx.config.head.boost` is `merge` and will apply to boosted links and forms.
+
+`htmx.config.head.other` will apply to non-boosted requests, and defaults to `none` (that is, new head information) will
+be ignored.
+
+You can also configure the head behavior using the [`hx-swap`](/attributes/hx-swap) attribute's `head` option.
+
 ### Progressive Enhancement {#progressive_enhancement}
 
 A feature of `hx-boost` is that it degrades gracefully if javascript is not enabled: the links and forms continue