Fix sub y extent when default extent set

c3.js

@@ -534,8 +534,10 @@
         yForText = $$.generateXYForText(areaIndices, barIndices, lineIndices, false);
 
         // Update sub domain
-        $$.subY.domain($$.y.domain());
-        $$.subY2.domain($$.y2.domain());
+        if (withY) {
+            $$.subY.domain($$.getYDomain(targetsToShow, 'y'));
+            $$.subY2.domain($$.getYDomain(targetsToShow, 'y2'));
+        }
 
         // tooltip
         $$.tooltip.style("display", "none");

spec/zoom-spec.js

@@ -0,0 +1,55 @@
+var describe = window.describe,
+    expect = window.expect,
+    it = window.it,
+    beforeEach = window.beforeEach;
+
+describe('c3 chart zoom', function () {
+    'use strict';
+
+    var chart, d3;
+
+    var args = {
+        data: {
+            columns: [
+                ['data1', 30, 200, 100, 400, 3150, 250],
+                ['data2', 50, 20, 10, 40, 15, 6025]
+            ]
+        },
+        axis: {
+            x: {
+                extent: [1, 2]
+            }
+        },
+        zoom: {
+            enable: true
+        },
+        subchart: {
+            show: true
+        }
+    };
+
+    beforeEach(function (done) {
+        chart = window.initChart(chart, args, done);
+        d3 = chart.internal.d3;
+    });
+
+    describe('default extent', function () {
+
+        it('should have default extent', function () {
+            var yDomain = chart.internal.y.domain(),
+                subYDomain = chart.internal.subY.domain(),
+                brushExtent = chart.internal.brush.extent(),
+                expectedYDomain = [-9, 219],
+                expectedSubYDomain = [-591.5, 6626.5],
+                expectedBrushExtent = [1, 2];
+            expect(yDomain[0]).toBe(expectedYDomain[0]);
+            expect(yDomain[1]).toBe(expectedYDomain[1]);
+            expect(subYDomain[0]).toBe(expectedSubYDomain[0]);
+            expect(subYDomain[1]).toBe(expectedSubYDomain[1]);
+            expect(brushExtent[0]).toBe(expectedBrushExtent[0]);
+            expect(brushExtent[1]).toBe(expectedBrushExtent[1]);
+        });
+        
+    });
+
+});

src/core.js

@@ -529,8 +529,10 @@ c3_chart_internal_fn.redraw = function (options, transitions) {
     yForText = $$.generateXYForText(areaIndices, barIndices, lineIndices, false);
 
     // Update sub domain
-    $$.subY.domain($$.y.domain());
-    $$.subY2.domain($$.y2.domain());
+    if (withY) {
+        $$.subY.domain($$.getYDomain(targetsToShow, 'y'));
+        $$.subY2.domain($$.getYDomain(targetsToShow, 'y2'));
+    }
 
     // tooltip
     $$.tooltip.style("display", "none");