--- a/svghmi/gen_index_xhtml.xslt	Wed Jun 03 13:31:55 2020 +0200
+++ b/svghmi/gen_index_xhtml.xslt	Thu Jun 04 11:14:21 2020 +0200
@@ -912,6 +912,8 @@
 </xsl:text>
     <xsl:text>    frequency = 10; /* FIXME arbitrary default max freq. Obtain from config ? */
 </xsl:text>
+    <xsl:text>    unsubscribable = false;
+</xsl:text>
     <xsl:text>    constructor(elt_id,args,indexes,members){
 </xsl:text>
     <xsl:text>        this.element_id = elt_id;
@@ -932,7 +934,7 @@
 </xsl:text>
     <xsl:text>        /* remove subsribers */
 </xsl:text>
-    <xsl:text>        for(let index of this.indexes){
+    <xsl:text>        if(!this.unsubscribable) for(let index of this.indexes){
 </xsl:text>
     <xsl:text>            let idx = index + this.offset;
 </xsl:text>
@@ -954,7 +956,7 @@
 </xsl:text>
     <xsl:text>        /* add this's subsribers */
 </xsl:text>
-    <xsl:text>        for(let index of this.indexes){
+    <xsl:text>        if(!this.unsubscribable) for(let index of this.indexes){
 </xsl:text>
     <xsl:text>            subscribers[index + new_offset].add(this);
 </xsl:text>
@@ -968,7 +970,7 @@
 </xsl:text>
     <xsl:text>    apply_cache() {
 </xsl:text>
-    <xsl:text>        for(let index of this.indexes){
+    <xsl:text>        if(!this.unsubscribable) for(let index of this.indexes){
 </xsl:text>
     <xsl:text>            /* dispatch current cache in newly opened page widgets */
 </xsl:text>
@@ -2292,11 +2294,7 @@
 </xsl:text>
       </xsl:when>
       <xsl:otherwise>
-        <xsl:text>        this.sub = function(){};
-</xsl:text>
-        <xsl:text>        this.unsub = function(){};
-</xsl:text>
-        <xsl:text>        this.apply_cache = function(){};
+        <xsl:text>        this.unsubscribable = true;
 </xsl:text>
       </xsl:otherwise>
     </xsl:choose>

--- a/svghmi/widget_jump.ysl2	Wed Jun 03 13:31:55 2020 +0200
+++ b/svghmi/widget_jump.ysl2	Thu Jun 04 11:14:21 2020 +0200
@@ -86,9 +86,7 @@
     |         this.disabled_elt_style = this.disabled_elt.getAttribute("style");
         }
         otherwise {
-    |         this.sub = function(){};
-    |         this.unsub = function(){};
-    |         this.apply_cache = function(){};
+    |         this.unsubscribable = true;
         }
     }
     |     },

--- a/svghmi/widgets_common.ysl2	Wed Jun 03 13:31:55 2020 +0200
+++ b/svghmi/widgets_common.ysl2	Thu Jun 04 11:14:21 2020 +0200
@@ -67,6 +67,7 @@
     class Widget {
         offset = 0;
         frequency = 10; /* FIXME arbitrary default max freq. Obtain from config ? */
+        unsubscribable = false;
         constructor(elt_id,args,indexes,members){
             this.element_id = elt_id;
             this.element = id(elt_id);
@@ -77,7 +78,7 @@
 
         unsub(){
             /* remove subsribers */
-            for(let index of this.indexes){
+            if(!this.unsubscribable) for(let index of this.indexes){
                 let idx = index + this.offset;
                 subscribers[idx].delete(this);
             }
@@ -88,14 +89,14 @@
             /* set the offset because relative */
             this.offset = new_offset;
             /* add this's subsribers */
-            for(let index of this.indexes){
+            if(!this.unsubscribable) for(let index of this.indexes){
                 subscribers[index + new_offset].add(this);
             }
             need_cache_apply.push(this); 
         }
 
         apply_cache() {
-            for(let index of this.indexes){
+            if(!this.unsubscribable) for(let index of this.indexes){
                 /* dispatch current cache in newly opened page widgets */
                 let realindex = index+this.offset;
                 let cached_val = cache[realindex];