made the output more compact...

Signed-off-by: Alex A. Naanou <alex.nanou@gmail.com>

README.md

@@ -2,8 +2,9 @@
 
 This extends the default JSON serialization adding the following:
 - Recursive data structure serialization
+- Sparse array serialization
 - `undefined`/`NaN` serialization
-- Serialization of `BigInt`'s, `Set`'s, `Map`'s
+- Serialization of `Infinity`, `BigInt`'s, `Set`'s, `Map`'s
 - Function serialization (off by default)
 - Deep and partial-deep cleen object copy
 
@@ -179,12 +180,6 @@ Default: 96
 The output of `.serialize(..)` is a strict superset of [standard JSON](https://www.json.org/json-en.html), 
 while the input format is a bit more relaxed than in several details.
 
-Extensions to JSON:
-- References
-- undefined / NaN
-- BigInt
-- Map / Set
-- Function
 
 ### Structural paths
 
@@ -202,7 +197,7 @@ structure traversed:
 Note that string path items are unambiguous and are always treated as 
 attributes.
 
-For examples see next section.
+An empty path indicates the root object.
 
 
 ### Referencing 
@@ -210,8 +205,6 @@ For examples see next section.
 If an object is encountered for a second time it will be serialized as 
 a reference by path to the first occurrence.
 
-An empty path indicates the root object.
-
 Format:
 ```bnf
 <ref> ::= 
@@ -254,10 +247,41 @@ serialize(new Map([['key', o]])) // -> 'Map([["key",[<REF[0,1]>]]])'
 ```
 
 
-### null types
+### Null types
+
+In addition to `null`, serialize.js adds support for `undefined` and 
+`NaN` which are stored as-is.
+
+Example:
+```javascript
+serialize([null, undefined, NaN]) // -> '[null,undefined,NaN]'
+```
+
+### Sparse arrays
+
+Sparse arrays are represented in the same way JavaScript handles them 
+syntactically.
+
+Example:
+```javascript
+serialize([,]) // -> '[,]'
+serialize([,,]) // -> '[,,]'
+```
+
+Note that trailing commas are ignored in the same way JavaScript ignores 
+them:
+```javascript
+// trailing comma...
+serialize([1,]) // -> '[1]'
+
+// sparse element...
+serialize([1,,]) // -> '[1,,]'
+```
 
 ### BigInt
 
+### Infinity
+
 ### Map / Set
 
 ### Functions
@@ -285,4 +309,4 @@ $ node ./test.js
 
 
 
-
+<!-- vim:set nowrap : -->

package.json

@@ -1,6 +1,6 @@
 {
   "name": "ig-serialize",
-  "version": "1.2.1",
+  "version": "1.3.0",
   "description": "experimental extended json serializaion...",
   "main": "serialize.js",
   "scripts": {

serialize.js

@@ -247,11 +247,13 @@ function(obj, path=[], seen=new Map(), indent, depth=0, options={}){
 	if(obj instanceof Array){
 		pre = '['
 		post = ']'
+		elems.length = obj.length
 		for(var i=0; i < obj.length; i++){
-			elems.push(
-				i in obj ?
-					_serialize(obj[i], [...path, i], seen, indent, depth+1, options)
-					: EMPTY) }
+			if(i in obj){
+				elems[i] = _serialize(obj[i], [...path, i], seen, indent, depth+1, options) } }
+		// add trailing coma if last elem is empty...
+		if(!(elems.length-1 in elems)){
+			elems.length++ }
 	} else if(obj instanceof Map){
 		pre = 'Map(['
 		post = '])'

test.js

@@ -82,13 +82,13 @@ var setups = test.Setups({
 	'array-empty': function(assert){
 		return ['[]', json] },
 	'array-sparse-a': function(assert){
-		return ['[<empty>]'] },
+		return ['[,]'] },
 	'array-sparse-b': function(assert){
-		return ['["a",<empty>]'] },
+		return ['["a",,]'] },
 	'array-sparse-c': function(assert){
-		return ['[<empty>,"a"]'] },
+		return ['[,"a"]'] },
 	'array-sparse-d': function(assert){
-		return ['[<empty>,1,<empty>,<empty>,2,<empty>]'] },
+		return ['[,1,,,2,,]'] },
 
 	'object-empty': function(assert){
 		return ['{}', json] },