Initial checkin

inc/theme.js

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+
+// Apply the chosen theme, and save that choice in a cookie on the user's browser
+//
+function SelectTheme(which) {
+	reloadCSS(which);
+	setCookie('theme', which, 10);	// Remember which theme they like
+}
+
+// Apply the CSS, which hosts the theme.
+//
+function reloadCSS(which) {
+	var links = document.getElementsByTagName("link");
+	for (var cl in links) {
+		var link = links[cl];
+		if (link.rel === "stylesheet")
+			link.href = "inc/theme-" + which + ".css";
+	}
+}
+
+//
+//
+function includeHTML() {
+  var z, i, elmnt, file, xhttp;
+  /* Loop through a collection of all HTML elements: */
+  z = document.getElementsByTagName("*");
+  for (i = 0; i < z.length; i++) {
+    elmnt = z[i];
+    /*search for elements with a certain atrribute:*/
+    file = elmnt.getAttribute("w3-include-html");
+    if (file) {
+      /* Make an HTTP request using the attribute value as the file name: */
+      xhttp = new XMLHttpRequest();
+      xhttp.onreadystatechange = function() {
+        if (this.readyState == 4) {
+          if (this.status == 200) {elmnt.innerHTML = this.responseText;}
+          if (this.status == 404) {elmnt.innerHTML = "Page not found.";}
+          /* Remove the attribute, and call this function once more: */
+          elmnt.removeAttribute("w3-include-html");
+          includeHTML();
+        }
+      }
+      xhttp.open("GET", file, true);
+      xhttp.send();
+      return;
+    }
+  }
+}
+
+// Save the cookie on the user's browser - this is for the color theme
+// and it has a timeout of some number of days, after which it expires.
+//
+function setCookie(cname, cvalue, exdays) {
+  const d = new Date();
+  d.setTime(d.getTime() + (exdays*24*60*60*1000));
+  let expires = "expires="+ d.toUTCString();
+  document.cookie = cname + "=" + cvalue + ";" + expires + ";path=/";
+}
+
+// Try to get the cookie. If the user has one, then it will use that
+// to apply a specific theme.
+//
+function getCookie(cname) {
+	let name = cname + "=";
+	let decodedCookie = decodeURIComponent(document.cookie);
+	let ca = decodedCookie.split(';');
+	for(let i = 0; i <ca.length; i++) {
+		let c = ca[i];
+		while (c.charAt(0) == ' ') {
+			c = c.substring(1);
+		}
+		if (c.indexOf(name) == 0) {
+			return c.substring(name.length, c.length);
+		}
+	}
+	return "";
+}
+