perf improvements in fx helpers

Author: etpinard

src/components/fx/helpers.js

@@ -17,14 +17,18 @@ exports.getSubplot = function getSubplot(trace) {
 
 // convenience functions for mapping all relevant axes
 exports.flat = function flat(subplots, v) {
-    var out = [];
-    for(var i = subplots.length; i > 0; i--) out.push(v);
+    var out = new Array(subplots.length);
+    for(var i = 0; i < subplots.length; i++) {
+        out[i] = v;
+    }
     return out;
 };
 
 exports.p2c = function p2c(axArray, v) {
-    var out = [];
-    for(var i = 0; i < axArray.length; i++) out.push(axArray[i].p2c(v));
+    var out = new Array(axArray.length);
+    for(var i = 0; i < axArray.length; i++) {
+        out[i] = axArray[i].p2c(v);
+    }
     return out;
 };