From 94bac893feb6617d61cf79f4321407c215224733 Mon Sep 17 00:00:00 2001
From: Victor Porof <victor.porof@gmail.com>
Date: Wed, 9 Sep 2020 14:27:08 +0200
Subject: [PATCH] Support sparse arrays (#95)

Signed-off-by: Victor Porof <victor.porof@gmail.com>
Co-authored-by: Ryuichi Okumura <okuryu@okuryu.com>
---
 index.js               | 16 ++++++++++++++--
 test/unit/serialize.js | 20 ++++++++++++++++++++
 2 files changed, 34 insertions(+), 2 deletions(-)

diff --git a/index.js b/index.js
index cf14df4..640db8f 100644
--- a/index.js
+++ b/index.js
@@ -11,7 +11,7 @@ var randomBytes = require('randombytes');
 // Generate an internal UID to make the regexp pattern harder to guess.
 var UID_LENGTH          = 16;
 var UID                 = generateUID();
-var PLACE_HOLDER_REGEXP = new RegExp('(\\\\)?"@__(F|R|D|M|S|U|I|B)-' + UID + '-(\\d+)__@"', 'g');
+var PLACE_HOLDER_REGEXP = new RegExp('(\\\\)?"@__(F|R|D|M|S|A|U|I|B)-' + UID + '-(\\d+)__@"', 'g');
 
 var IS_NATIVE_CODE_REGEXP = /\{\s*\[native code\]\s*\}/g;
 var IS_PURE_FUNCTION = /function.*?\(/;
@@ -68,6 +68,7 @@ module.exports = function serialize(obj, options) {
     var dates     = [];
     var maps      = [];
     var sets      = [];
+    var arrays    = [];
     var undefs    = [];
     var infinities= [];
     var bigInts = [];
@@ -106,6 +107,13 @@ module.exports = function serialize(obj, options) {
             if(origValue instanceof Set) {
                 return '@__S-' + UID + '-' + (sets.push(origValue) - 1) + '__@';
             }
+
+            if(origValue instanceof Array) {
+                var isSparse = origValue.filter(function(){return true}).length !== origValue.length;
+                if (isSparse) {
+                    return '@__A-' + UID + '-' + (arrays.push(origValue) - 1) + '__@';
+                }
+            }
         }
 
         if (type === 'function') {
@@ -197,7 +205,7 @@ module.exports = function serialize(obj, options) {
         str = str.replace(UNSAFE_CHARS_REGEXP, escapeUnsafeChars);
     }
 
-    if (functions.length === 0 && regexps.length === 0 && dates.length === 0 && maps.length === 0 && sets.length === 0 && undefs.length === 0 && infinities.length === 0 && bigInts.length === 0) {
+    if (functions.length === 0 && regexps.length === 0 && dates.length === 0 && maps.length === 0 && sets.length === 0 && arrays.length === 0 && undefs.length === 0 && infinities.length === 0 && bigInts.length === 0) {
         return str;
     }
 
@@ -228,6 +236,10 @@ module.exports = function serialize(obj, options) {
             return "new Set(" + serialize(Array.from(sets[valueIndex].values()), options) + ")";
         }
 
+        if (type === 'A') {
+            return "Array.prototype.slice.call(" + serialize(Object.assign({ length: arrays[valueIndex].length }, arrays[valueIndex]), options) + ")";
+        }
+
         if (type === 'U') {
             return 'undefined'
         }
diff --git a/test/unit/serialize.js b/test/unit/serialize.js
index a618dae..bd24070 100644
--- a/test/unit/serialize.js
+++ b/test/unit/serialize.js
@@ -392,6 +392,26 @@ describe('serialize( obj )', function () {
         });
     });
 
+    describe('sparse arrays', function () {
+        it('should serialize sparse arrays', function () {
+            var a = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
+            delete a[0];
+            a.length = 3;
+            a[5] = "wat"
+            expect(serialize(a)).to.be.a('string').equal('Array.prototype.slice.call({"1":2,"2":3,"5":"wat","length":6})');
+            expect(serialize({t: [a]})).to.be.a('string').equal('{"t":[Array.prototype.slice.call({"1":2,"2":3,"5":"wat","length":6})]}');
+        });
+
+        it('should deserialize a sparse array', function () {
+            var a = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
+            delete a[0];
+            a.length = 3;
+            a[5] = "wat"
+            var b = eval(serialize(a));
+            expect(b).to.be.a('Array').deep.equal([ , 2, 3, , , 'wat' ]);
+        });
+    });
+
     describe('Infinity', function () {
         it('should serialize Infinity', function () {
             expect(serialize(Infinity)).to.equal('Infinity');