split bbox once, as suggested by @tomkralidis

pycsw/ogc/api/templates/items.html

@@ -211,15 +211,15 @@
 function facet(val){
   location.href="{{updateurl('facets','facetprop')}}".replace('facetprop',val);
 }
+var bbox;
 //if url has a bbox, enable the spatial filter 
-{% if 'bbox' in attrs.keys() and (attrs['bbox'].split('%2C')|length) == 4 %}
-var bbox = [
-          [{{ attrs['bbox'].split('%2C')[1] }}, {{ attrs['bbox'].split('%2C')[0] }}], 
-          [{{ attrs['bbox'].split('%2C')[3] }}, {{ attrs['bbox'].split('%2C')[2] }}]
-        ]
-{% else %}
-var bbox = null;
-{% endif %}
+{% if 'bbox' in attrs.keys() %}
+{% set bbox_tokens = attrs['bbox'].split('%2C') %}
+{% if bbox_tokens|length == 4 %}
+bbox = [[{{ 
+  bbox_tokens[1] }}, {{ bbox_tokens[0] }}], [{{ 
+  bbox_tokens[3] }}, {{ bbox_tokens[2] }}]]
+{% endif %}{% endif %}
 
 //if filter enabled, apply the spatial filter
 function apply_spatial_filter(){