From f7f99e0be19fcfc10990cd2c14ee9bb21495dded Mon Sep 17 00:00:00 2001
From: Huu Nghia NGUYEN <nhnghia@me.com>
Date: Fri, 22 Jan 2016 16:31:55 +0100
Subject: [PATCH] gh-1554 firefox takes much time to concat a big array

---
 c3.js | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/c3.js b/c3.js
index 3c7b540..7d400cc 100644
--- a/c3.js
+++ b/c3.js
@@ -1993,12 +1993,13 @@
         return Math.sqrt(Math.pow(x - pos[xIndex], 2) + Math.pow(y - pos[yIndex], 2));
     };
     c3_chart_internal_fn.convertValuesToStep = function (values) {
-        var converted = [].concat(values), i;
 
         if (!this.isCategorized()) {
             return values;
         }
-
+        
+        var converted = values.slice(0), i;
+        
         for (i = values.length + 1; 0 < i; i--) {
             converted[i] = converted[i - 1];
         }