diff --git a/src/basic/Rectangle.js b/src/basic/Rectangle.js
index 376e7589..85d3e890 100644
--- a/src/basic/Rectangle.js
+++ b/src/basic/Rectangle.js
@@ -880,7 +880,7 @@ var LinkedRectangle = Rectangle.extend({
 				// afterwards here, only once per change.
 				this._dontNotify = true;
 				proto[name].apply(this, arguments);
-				delete this._dontNotify;
+				this._dontNotify = false;
 				this._owner[this._setter](this);
 			};
 		}, /** @lends Rectangle# */{
diff --git a/src/core/Base.js b/src/core/Base.js
index aa6fe49c..4fd9511e 100644
--- a/src/core/Base.js
+++ b/src/core/Base.js
@@ -191,9 +191,9 @@ Base.inject(/** @lends Base# */{
 				// Have arguments.__read point to the amount of args read in the
 				// last read() call
 				list.__read = obj.__read;
-				delete obj.__read;
+				obj.__read = undefined;
 				if (options)
-					delete obj.__options;
+					obj.__options = undefined;
 			}
 			return obj;
 		},
@@ -491,9 +491,9 @@ Base.inject(/** @lends Base# */{
 				if (items)
 					args.push.apply(args, items);
 				var removed = list.splice.apply(list, args);
-				// Delete the indices of the removed items
+				// Erase the indices of the removed items
 				for (var i = 0, l = removed.length; i < l; i++)
-					delete removed[i]._index;
+					removed[i]._index = undefined;
 				// Adjust the indices of the items above.
 				for (var i = index + amount, l = list.length; i < l; i++)
 					list[i]._index = i;
diff --git a/src/item/Group.js b/src/item/Group.js
index a478221e..179bfe77 100644
--- a/src/item/Group.js
+++ b/src/item/Group.js
@@ -106,7 +106,7 @@ var Group = Item.extend(/** @lends Group# */{
 		}
 		if (flags & (/*#=*/ ChangeFlag.HIERARCHY | /*#=*/ ChangeFlag.CLIPPING)) {
 			// Clear cached clip item whenever hierarchy changes
-			delete this._clipItem;
+			this._clipItem = undefined;
 		}
 	},
 
diff --git a/src/path/CompoundPath.js b/src/path/CompoundPath.js
index 3b648f0d..3d6725a5 100644
--- a/src/path/CompoundPath.js
+++ b/src/path/CompoundPath.js
@@ -103,9 +103,9 @@ var CompoundPath = PathItem.extend(/** @lends CompoundPath# */{
 
 	_changed: function _changed(flags) {
 		_changed.base.call(this, flags);
-		// Delete cached native Path
+		// Clear cached native Path
 		if (flags & (/*#=*/ ChangeFlag.HIERARCHY | /*#=*/ ChangeFlag.GEOMETRY))
-			delete this._currentPath;
+			this._currentPath = undefined;
 	},
 
 	insertChildren: function insertChildren(index, items, _preserve) {
diff --git a/src/path/Curve.js b/src/path/Curve.js
index 2331a317..f89cfeaf 100644
--- a/src/path/Curve.js
+++ b/src/path/Curve.js
@@ -98,8 +98,7 @@ var Curve = Base.extend(/** @lends Curve# */{
 
 	_changed: function() {
 		// Clear cached values.
-		delete this._length;
-		delete this._bounds;
+		this._length = this._bounds = undefined;
 	},
 
 	/**
diff --git a/src/path/Path.js b/src/path/Path.js
index 4eb8bd69..f8366f04 100644
--- a/src/path/Path.js
+++ b/src/path/Path.js
@@ -135,11 +135,10 @@ var Path = PathItem.extend(/** @lends Path# */{
 	_changed: function _changed(flags) {
 		_changed.base.call(this, flags);
 		if (flags & /*#=*/ ChangeFlag.GEOMETRY) {
-			// Delete cached native Path
-			delete (this._compound ? this._parent : this)._currentPath;
-			delete this._length;
+			// Clear cached native Path
+			(this._compound ? this._parent : this)._currentPath = undefined;
 			// Clockwise state becomes undefined as soon as geometry changes.
-			delete this._clockwise;
+			this._length = this._clockwise = undefined;
 			// Curves are no longer valid
 			if (this._curves) {
 				for (var i = 0, l = this._curves.length; i < l; i++)
@@ -148,7 +147,7 @@ var Path = PathItem.extend(/** @lends Path# */{
 		} else if (flags & /*#=*/ ChangeFlag.STROKE) {
 			// TODO: We could preserve the purely geometric bounds that are not
 			// affected by stroke: _bounds.bounds and _bounds.handleBounds
-			delete this._bounds;
+			this._bounds = undefined;
 		}
 	},
 
@@ -167,7 +166,7 @@ var Path = PathItem.extend(/** @lends Path# */{
 		this._segments.length = 0;
 		this._selectedSegmentState = 0;
 		// Calculate new curves next time we call getCurves()
-		delete this._curves;
+		this._curves = undefined;
 		this._add(Segment.readAll(segments));
 		if (fullySelected)
 			this.setFullySelected(true);
@@ -701,8 +700,7 @@ var Path = PathItem.extend(/** @lends Path# */{
 			if (segment._selectionState)
 				this._updateSelection(segment, segment._selectionState, 0);
 			// Clear the indices and path references of the removed segments
-			delete segment._index;
-			delete segment._path;
+			segment._index = segment._path = null;
 		}
 		// Adjust the indices of the segments above.
 		for (var i = from, l = segments.length; i < l; i++)
@@ -1144,7 +1142,7 @@ var Path = PathItem.extend(/** @lends Path# */{
 			segment._index = i;
 		}
 		// Clear curves since it all has changed.
-		delete this._curves;
+		this._curves = null;
 		// Flip clockwise state if it's defined
 		if (this._clockwise !== undefined)
 			this._clockwise = !this._clockwise;
diff --git a/src/path/PathItem.Boolean.js b/src/path/PathItem.Boolean.js
index 0ec05826..8cae7558 100644
--- a/src/path/PathItem.Boolean.js
+++ b/src/path/PathItem.Boolean.js
@@ -192,7 +192,7 @@ PathItem.inject(new function() {
 				path.remove();
 			}
 		}
-		// Delete the proxies
+		// Remove the proxies
 		path1.remove();
 		path2.remove();
 		// And then, we are done.
diff --git a/src/project/Symbol.js b/src/project/Symbol.js
index 7db868b5..c13b4fd9 100644
--- a/src/project/Symbol.js
+++ b/src/project/Symbol.js
@@ -121,7 +121,7 @@ var Symbol = Base.extend(/** @lends Symbol# */{
 			item = item.clone();
 		// Remove previous definition's reference to this symbol
 		if (this._definition)
-			delete this._definition._parentSymbol;
+			this._definition._parentSymbol = null;
 		this._definition = item;
 		// Remove item from DOM, as it's embedded in Symbol now.
 		item.remove();
diff --git a/src/style/Gradient.js b/src/style/Gradient.js
index c8f58400..93bd9426 100644
--- a/src/style/Gradient.js
+++ b/src/style/Gradient.js
@@ -113,7 +113,7 @@ var Gradient = Base.extend(/** @lends Gradient# */{
 		if (index != -1) {
 			this._owners.splice(index, 1);
 			if (this._owners.length === 0)
-				delete this._owners;
+				this._owners = undefined;
 		}
 	},
 
@@ -142,7 +142,7 @@ var Gradient = Base.extend(/** @lends Gradient# */{
 		// this gradient as their owner.
 		if (this.stops) {
 			for (var i = 0, l = this._stops.length; i < l; i++)
-				delete this._stops[i]._owner;
+				this._stops[i]._owner = undefined;
 		}
 		if (stops.length < 2)
 			throw new Error(
diff --git a/src/style/Style.js b/src/style/Style.js
index 8719f9bc..82826623 100644
--- a/src/style/Style.js
+++ b/src/style/Style.js
@@ -147,7 +147,7 @@ var Style = Base.extend(new function() {
 				if (old != value) {
 					if (isColor) {
 						if (old)
-							delete old._owner;
+							old._owner = undefined;
 						if (value && value.constructor === Color) {
 							// Clone color if it already has an owner.
 							// NOTE: If value is not a Color, it is only