Support: improve support properties computation

* Remove div from the memory if it is not needed anymore

* Make `computeStyleTests` method a singleton

Fixes gh-3018
Closes gh-3021

1 files changed, 15 insertions, 19 deletions

diff --git a/src/css/support.js b/src/css/support.js
index 1150485bf..0c02b71d7 100644
--- a/src/css/support.js
+++ b/src/css/support.js
@@ -28,6 +28,12 @@ define( [
 	// Executing both pixelPosition & boxSizingReliable tests require only one layout
 	// so they're executed at the same time to save the second computation.
 	function computeStyleTests() {
+
+		// This is a singleton, we need to execute it only once
+		if ( !div ) {
+			return;
+		}
+
 		div.style.cssText =
 			"box-sizing:border-box;" +
 			"position:relative;display:block;" +
@@ -38,6 +44,8 @@ define( [
 
 		var divStyle = window.getComputedStyle( div );
 		pixelPositionVal = divStyle.top !== "1%";
+
+		// Support: Android 4.0 - 4.3 only, Firefox <=3 - 44+
 		reliableMarginLeftVal = divStyle.marginLeft === "2px";
 		boxSizingReliableVal = divStyle.width === "4px";
 
@@ -47,39 +55,27 @@ define( [
 		pixelMarginRightVal = divStyle.marginRight === "4px";
 
 		documentElement.removeChild( container );
+
+		// Nullify the div so it wouldn't be stored in the memory and
+		// it will also be a sign that checks already performed
+		div = null;
 	}
 
 	jQuery.extend( support, {
 		pixelPosition: function() {
-
-			// This test is executed only once but we still do memoizing
-			// since we can use the boxSizingReliable pre-computing.
-			// No need to check if the test was already performed, though.
 			computeStyleTests();
 			return pixelPositionVal;
 		},
 		boxSizingReliable: function() {
-			if ( boxSizingReliableVal == null ) {
-				computeStyleTests();
-			}
+			computeStyleTests();
 			return boxSizingReliableVal;
 		},
 		pixelMarginRight: function() {
-
-			// Support: Android 4.0 - 4.3 only
-			// We're checking for boxSizingReliableVal here instead of pixelMarginRightVal
-			// since that compresses better and they're computed together anyway.
-			if ( boxSizingReliableVal == null ) {
-				computeStyleTests();
-			}
+			computeStyleTests();
 			return pixelMarginRightVal;
 		},
 		reliableMarginLeft: function() {
-
-			// Support: Android 4.0 - 4.3 only, Firefox <=3 - 44+
-			if ( boxSizingReliableVal == null ) {
-				computeStyleTests();
-			}
+			computeStyleTests();
 			return reliableMarginLeftVal;
 		}
 	} );