added comments, made things `const`

sanitizer/_synthesize_analysis.js

@@ -21,6 +21,10 @@ function isPostalCodeOnly(parsed_text) {
           parsed_text.hasOwnProperty('postalcode');
 }
 
+// figure out which field contains the probable house number, prefer number
+// libpostal parses some inputs, like `3370 cobbe ave`, as a postcode+street
+// so because we're treating the entire field as a street address, it's safe
+// to assume that an identified postcode is actually a house number.
 function getHouseNumberField(analyzed_address) {
   for (var field of ['number', 'postalcode']) {
     if (analyzed_address.hasOwnProperty(field)) {
@@ -54,21 +58,31 @@ function sanitize( raw, clean ){
   }
 
   if (clean.parsed_text.hasOwnProperty('address')) {
-    var analyzed_address = text_analyzer.parse(clean.parsed_text.address);
+    const analyzed_address = text_analyzer.parse(clean.parsed_text.address);
 
     const house_number_field = getHouseNumberField(analyzed_address);
 
+    // if we're fairly certain that libpostal identified a house number
+    // (from either the house_number or postcode field), place it into the
+    // number field and remove the first instance of that value from address
+    // and assign to street
+    // eg - '1090 N Charlotte St' becomes number=1090 and street=N Charlotte St
     if (house_number_field) {
       clean.parsed_text.number = analyzed_address[house_number_field];
 
+      // remove the first instance of the number and trim whitespace
       clean.parsed_text.street = _.trim(_.replace(clean.parsed_text.address, clean.parsed_text.number, ''));
-      delete clean.parsed_text.address;
 
     } else {
+      // otherwise no house number was identifiable, so treat the entire input
+      // as a street
       clean.parsed_text.street = clean.parsed_text.address;
-      delete clean.parsed_text.address;
+
     }
 
+    // the address field no longer means anything since it's been parsed, so remove it
+    delete clean.parsed_text.address;
+
   }
 
   return messages;