brush.clamp: return null if there are no scales.

Similarly, if there are no scales, setting a clamp does nothing.

For consistency with brush.extent.

d3.js

@@ -8047,8 +8047,8 @@ d3 = function() {
       return brush;
     };
     brush.clamp = function(z) {
-      if (!arguments.length) return x && y ? clamp : clamp[+!x];
-      if (x && y) clamp = [ !!z[0], !!z[1] ]; else clamp[+!x] = !!z;
+      if (!arguments.length) return x && y ? clamp : x || y ? clamp[+!x] : null;
+      if (x && y) clamp = [ !!z[0], !!z[1] ]; else if (x || y) clamp[+!x] = !!z;
       return brush;
     };
     brush.extent = function(z) {

src/svg/brush.js

@@ -287,9 +287,9 @@ d3.svg.brush = function() {
   };
 
   brush.clamp = function(z) {
-    if (!arguments.length) return x && y ? clamp : clamp[+!x];
+    if (!arguments.length) return x && y ? clamp : x || y ? clamp[+!x] : null;
     if (x && y) clamp = [!!z[0], !!z[1]];
-    else clamp[+!x] = !!z;
+    else if (x || y) clamp[+!x] = !!z;
     return brush;
   };
 

test/svg/brush-test.js

@@ -22,6 +22,9 @@ suite.addBatch({
     },
 
     "clamp": {
+      "returns null when no scales are attached": function(brush) {
+        assert.isNull(brush().clamp());
+      },
       "returns a single boolean if only x is defined": function(brush) {
         var b = brush().x(_.scale.linear());
         assert.isTrue(b.clamp());