Track DOM content loaded for ready() function (#1688)

Track whether DOMContentLoaded has been fired

src/htmx.js

@@ -3603,9 +3603,22 @@ return (function () {
         //====================================================================
         // Initialization
         //====================================================================
+        var isReady = false
+        getDocument().addEventListener('DOMContentLoaded', function() {
+            isReady = true
+        })
 
+        /**
+         * Execute a function now if DOMContentLoaded has fired, otherwise listen for it.
+         *
+         * This function uses isReady because there is no realiable way to ask the browswer whether
+         * the DOMContentLoaded event has already been fired; there's a gap between DOMContentLoaded
+         * firing and readystate=complete.
+         */
         function ready(fn) {
-            if (getDocument().readyState === 'complete') {
+            // Checking readyState here is a failsafe in case the htmx script tag entered the DOM by
+            // some means other than the initial page load.
+            if (isReady || getDocument().readyState === 'complete') {
                 fn();
             } else {
                 getDocument().addEventListener('DOMContentLoaded', fn);