Add mutating extent extend, for performance

js/id/core/relation.js

@@ -25,14 +25,15 @@ _.extend(iD.Relation.prototype, {
             if (memo && memo[this.id]) return iD.geo.Extent();
             memo = memo || {};
             memo[this.id] = true;
-            return this.members.reduce(function(extent, member) {
-                member = resolver.hasEntity(member.id);
+
+            var extent = iD.geo.Extent();
+            for (var i = 0; i < this.members.length; i++) {
+                var member = resolver.hasEntity(this.members[i].id);
                 if (member) {
-                    return extent.extend(member.extent(resolver, memo));
-                } else {
-                    return extent;
+                    extent._extend(member.extent(resolver, memo));
                 }
-            }, iD.geo.Extent());
+            }
+            return extent;
         });
     },
 

js/id/core/way.js

@@ -14,14 +14,14 @@ _.extend(iD.Way.prototype, {
 
     extent: function(resolver) {
         return resolver.transient(this, 'extent', function() {
-            return this.nodes.reduce(function(extent, id) {
-                var node = resolver.hasEntity(id);
+            var extent = iD.geo.Extent();
+            for (var i = 0; i < this.nodes.length; i++) {
+                var node = resolver.hasEntity(this.nodes[i]);
                 if (node) {
-                    return extent.extend(node.extent());
-                } else {
-                    return extent;
+                    extent._extend(node.extent());
                 }
-            }, iD.geo.Extent());
+            };
+            return extent;
         });
     },
 

js/id/geo/extent.js

@@ -22,6 +22,13 @@ _.extend(iD.geo.Extent.prototype, {
                               Math.max(obj[1][1], this[1][1])]);
     },
 
+    _extend: function(extent) {
+        this[0][0] = Math.min(extent[0][0], this[0][0]);
+        this[0][1] = Math.min(extent[0][1], this[0][1]);
+        this[1][0] = Math.max(extent[1][0], this[1][0]);
+        this[1][1] = Math.max(extent[1][1], this[1][1]);
+    },
+
     area: function() {
         return Math.abs((this[1][0] - this[0][0]) * (this[1][1] - this[0][1]));
     },

test/spec/geo/extent.js

@@ -87,6 +87,18 @@ describe("iD.geo.Extent", function () {
         });
     });
 
+    describe("#_extend", function () {
+        it("extends self to the minimal extent containing self and the given extent", function () {
+            var e = iD.geo.Extent();
+            e._extend([[0, 0], [5, 10]]);
+            expect(e).to.eql([[0, 0], [5, 10]]);
+
+            e = iD.geo.Extent([0, 0], [0, 0]);
+            e._extend([[4, -1], [5, 10]]);
+            expect(e).to.eql([[0, -1], [5, 10]]);
+        });
+    });
+
     describe('#intersects', function () {
         it("returns true for a point inside self", function () {
             expect(iD.geo.Extent([0, 0], [5, 5]).intersects([2, 2])).to.be.true;