text: function Axis(owner) {
      API.call(this, owner);
  }
  
  inherit(API, Axis);
  
  Axis.prototype.init = function init() {
  
      var $$ = this.owner, config = $$.config, main = $$.main;
      $$.axes.x = main.append("g")
          .attr("class", CLASS.axis + ' ' + CLASS.axisX)
          .attr("clip-path", $$.clipPathForXAxis)
          .attr("transform", $$.getTranslate('x'))
          .style("visibility", config.axis_x_show ? 'visible' : 'hidden');
      $$.axes.x.append("text")
          .attr("class", CLASS.axisXLabel)
          .attr("transform", config.axis_rotated ? "rotate(-90)" : "")
          .style("text-anchor", this.textAnchorForXAxisLabel.bind(this));
      $$.axes.y = main.append("g")
          .attr("class", CLASS.axis + ' ' + CLASS.axisY)
          .attr("clip-path", config.axis_y_inner ? "" : $$.clipPathForYAxis)
          .attr("transform", $$.getTranslate('y'))
          .style("visibility", config.axis_y_show ? 'visible' : 'hidden');
      $$.axes.y.append("text")
          .attr("class", CLASS.axisYLabel)
          .attr("transform", config.axis_rotated ? "" : "rotate(-90)")
          .style("text-anchor", this.textAnchorForYAxisLabel.bind(this));
  
      $$.axes.y2 = main.append("g")
          .attr("class", CLASS.axis + ' ' + CLASS.axisY2)
          // clip-path?
          .attr("transform", $$.getTranslate('y2'))
          .style("visibility", config.axis_y2_show ? 'visible' : 'hidden');
      $$.axes.y2.append("text")
          .attr("class", CLASS.axisY2Label)
          .attr("transform", config.axis_rotated ? "" : "rotate(-90)")
          .style("text-anchor", this.textAnchorForY2AxisLabel.bind(this));
  };
  Axis.prototype.getXAxis = function getXAxis(scale, orient, tickFormat, tickValues, withOuterTick, withoutTransition, withoutRotateTickText) {
      var $$ = this.owner, config = $$.config,
          axisParams = {
              isCategory: $$.isCategorized(),
              withOuterTick: withOuterTick,
              tickMultiline: config.axis_x_tick_multiline,
              tickWidth: config.axis_x_tick_width,
              tickTextRotate: withoutRotateTickText ? 0 : config.axis_x_tick_rotate,
              withoutTransition: withoutTransition,
          },
          axis = c3_axis($$.d3, axisParams).scale(scale).orient(orient);
  
      if ($$.isTimeSeries() && tickValues && typeof tickValues !== "function") {
          tickValues = tickValues.map(function (v) { return $$.parseDate(v); });
      }
  
      // Set tick
      axis.tickFormat(tickFormat).tickValues(tickValues);
      if ($$.isCategorized()) {
          axis.tickCentered(config.axis_x_tick_centered);
          if (isEmpty(config.axis_x_tick_culling)) {
              config.axis_x_tick_culling = false;
          }
      }
  
      return axis;
  };
  Axis.prototype.updateXAxisTickValues = function updateXAxisTickValues(targets, axis) {
      var $$ = this.owner, config = $$.config, tickValues;
      if (config.axis_x_tick_fit || config.axis_x_tick_count) {
          tickValues = this.generateTickValues($$.mapTargetsToUniqueXs(targets), config.axis_x_tick_count, $$.isTimeSeries());
      }
      if (axis) {
          axis.tickValues(tickValues);
      } else {
          $$.xAxis.tickValues(tickValues);
          $$.subXAxis.tickValues(tickValues);
      }
      return tickValues;
  };
  Axis.prototype.getYAxis = function getYAxis(scale, orient, tickFormat, tickValues, withOuterTick, withoutTransition, withoutRotateTickText) {
      var $$ = this.owner, config = $$.config,
          axisParams = {
              withOuterTick: withOuterTick,
              withoutTransition: withoutTransition,
              tickTextRotate: withoutRotateTickText ? 0 : config.axis_y_tick_rotate
          },
          axis = c3_axis($$.d3, axisParams).scale(scale).orient(orient).tickFormat(tickFormat);
      if ($$.isTimeSeriesY()) {
          axis.ticks($$.d3.time[config.axis_y_tick_time_value], config.axis_y_tick_time_interval);
      } else {
          axis.tickValues(tickValues);
      }
      return axis;
  };
  Axis.prototype.getId = function getId(id) {
      var config = this.owner.config;
      return id in config.data_axes ? config.data_axes[id] : 'y';
  };
  Axis.prototype.getXAxisTickFormat = function getXAxisTickFormat() {
      var $$ = this.owner, config = $$.config,
          format = $$.isTimeSeries() ? $$.defaultAxisTimeFormat : $$.isCategorized() ? $$.categoryName : function (v) { return v < 0 ? v.toFixed(0) : v; };
      if (config.axis_x_tick_format) {
          if (isFunction(config.axis_x_tick_format)) {
              format = config.axis_x_tick_format;
          } else if ($$.isTimeSeries()) {
              format = function (date) {
                  return date ? $$.axisTimeFormat(config.axis_x_tick_format)(date) : "";
              };
          }
      }
      return isFunction(format) ? function (v) { return format.call($$, v); } : format;
  };
  Axis.prototype.getTickValues = function getTickValues(tickValues, axis) {
      return tickValues ? tickValues : axis ? axis.tickValues() : undefined;
  };
  Axis.prototype.getXAxisTickValues = function getXAxisTickValues() {
      return this.getTickValues(this.owner.config.axis_x_tick_values, this.owner.xAxis);
  };
  Axis.prototype.getYAxisTickValues = function getYAxisTickValues() {
      return this.getTickValues(this.owner.config.axis_y_tick_values, this.owner.yAxis);
  };
  Axis.prototype.getY2AxisTickValues = function getY2AxisTickValues() {
      return this.getTickValues(this.owner.config.axis_y2_tick_values, this.owner.y2Axis);
  };
  Axis.prototype.getLabelOptionByAxisId = function getLabelOptionByAxisId(axisId) {
      var $$ = this.owner, config = $$.config, option;
      if (axisId === 'y') {
          option = config.axis_y_label;
      } else if (axisId === 'y2') {
          option = config.axis_y2_label;
      } else if (axisId === 'x') {
          option = config.axis_x_label;
      }
      return option;
  };
  Axis.prototype.getLabelText = function getLabelText(axisId) {
      var option = this.getLabelOptionByAxisId(axisId);
      return isString(option) ? option : option ? option.text : null;
  };
  Axis.prototype.setLabelText = function setLabelText(axisId, text) {
      var $$ = this.owner, config = $$.config,
          option = this.getLabelOptionByAxisId(axisId);
      if (isString(option)) {
          if (axisId === 'y') {
              config.axis_y_label = text;
          } else if (axisId === 'y2') {
              config.axis_y2_label = text;
          } else if (axisId === 'x') {
              config.axis_x_label = text;
          }
      } else if (option) {
          option.text = text;
      }
  };
  Axis.prototype.getLabelPosition = function getLabelPosition(axisId, defaultPosition) {
      var option = this.getLabelOptionByAxisId(axisId),
          position = (option && typeof option === 'object' && option.position) ? option.position : defaultPosition;
      return {
          isInner: position.indexOf('inner') >= 0,
          isOuter: position.indexOf('outer') >= 0,
          isLeft: position.indexOf('left') >= 0,
          isCenter: position.indexOf('center') >= 0,
          isRight: position.indexOf('right') >= 0,
          isTop: position.indexOf('top') >= 0,
          isMiddle: position.indexOf('middle') >= 0,
          isBottom: position.indexOf('bottom') >= 0
      };
  };
  Axis.prototype.getXAxisLabelPosition = function getXAxisLabelPosition() {
      return this.getLabelPosition('x', this.owner.config.axis_rotated ? 'inner-top' : 'inner-right');
  };
  Axis.prototype.getYAxisLabelPosition = function getYAxisLabelPosition() {
      return this.getLabelPosition('y', this.owner.config.axis_rotated ? 'inner-right' : 'inner-top');
  };
  Axis.prototype.getY2AxisLabelPosition = function getY2AxisLabelPosition() {
      return this.getLabelPosition('y2', this.owner.config.axis_rotated ? 'inner-right' : 'inner-top');
  };
  Axis.prototype.getLabelPositionById = function getLabelPositionById(id) {
      return id === 'y2' ? this.getY2AxisLabelPosition() : id === 'y' ? this.getYAxisLabelPosition() : this.getXAxisLabelPosition();
  };
  Axis.prototype.textForXAxisLabel = function textForXAxisLabel() {
      return this.getLabelText('x');
  };
  Axis.prototype.textForYAxisLabel = function textForYAxisLabel() {
      return this.getLabelText('y');
  };
  Axis.prototype.textForY2AxisLabel = function textForY2AxisLabel() {
      return this.getLabelText('y2');
  };
  Axis.prototype.xForAxisLabel = function xForAxisLabel(forHorizontal, position) {
      var $$ = this.owner;
      if (forHorizontal) {
          return position.isLeft ? 0 : position.isCenter ? $$.width / 2 : $$.width;
      } else {
          return position.isBottom ? -$$.height : position.isMiddle ? -$$.height / 2 : 0;
      }
  };
  Axis.prototype.dxForAxisLabel = function dxForAxisLabel(forHorizontal, position) {
      if (forHorizontal) {
          return position.isLeft ? "0.5em" : position.isRight ? "-0.5em" : "0";
      } else {
          return position.isTop ? "-0.5em" : position.isBottom ? "0.5em" : "0";
      }
  };
  Axis.prototype.textAnchorForAxisLabel = function textAnchorForAxisLabel(forHorizontal, position) {
      if (forHorizontal) {
          return position.isLeft ? 'start' : position.isCenter ? 'middle' : 'end';
      } else {
          return position.isBottom ? 'start' : position.isMiddle ? 'middle' : 'end';
      }
  };
  Axis.prototype.xForXAxisLabel = function xForXAxisLabel() {
      return this.xForAxisLabel(!this.owner.config.axis_rotated, this.getXAxisLabelPosition());
  };
  Axis.prototype.xForYAxisLabel = function xForYAxisLabel() {
      return this.xForAxisLabel(this.owner.config.axis_rotated, this.getYAxisLabelPosition());
  };
  Axis.prototype.xForY2AxisLabel = function xForY2AxisLabel() {
      return this.xForAxisLabel(this.owner.config.axis_rotated, this.getY2AxisLabelPosition());
  };
  Axis.prototype.dxForXAxisLabel = function dxForXAxisLabel() {
      return this.dxForAxisLabel(!this.owner.config.axis_rotated, this.getXAxisLabelPosition());
  };
  Axis.prototype.dxForYAxisLabel = function dxForYAxisLabel() {
      return this.dxForAxisLabel(this.owner.config.axis_rotated, this.getYAxisLabelPosition());
  };
  Axis.prototype.dxForY2AxisLabel = function dxForY2AxisLabel() {
      return this.dxForAxisLabel(this.owner.config.axis_rotated, this.getY2AxisLabelPosition());
  };
  Axis.prototype.dyForXAxisLabel = function dyForXAxisLabel() {
      var $$ = this.owner, config = $$.config,
          position = this.getXAxisLabelPosition();
      if (config.axis_rotated) {
          return position.isInner ? "1.2em" : -25 - this.getMaxTickWidth('x');
      } else {
          return position.isInner ? "-0.5em" : config.axis_x_height ? config.axis_x_height - 10 : "3em";
      }
  };
  Axis.prototype.dyForYAxisLabel = function dyForYAxisLabel() {
      var $$ = this.owner,
          position = this.getYAxisLabelPosition();
      if ($$.config.axis_rotated) {
          return position.isInner ? "-0.5em" : "3em";
      } else {
          return position.isInner ? "1.2em" : -10 - ($$.config.axis_y_inner ? 0 : (this.getMaxTickWidth('y') + 10));
      }
  };
  Axis.prototype.dyForY2AxisLabel = function dyForY2AxisLabel() {
      var $$ = this.owner,
          position = this.getY2AxisLabelPosition();
      if ($$.config.axis_rotated) {
          return position.isInner ? "1.2em" : "-2.2em";
      } else {
          return position.isInner ? "-0.5em" : 15 + ($$.config.axis_y2_inner ? 0 : (this.getMaxTickWidth('y2') + 15));
      }
  };
  Axis.prototype.textAnchorForXAxisLabel = function textAnchorForXAxisLabel() {
      var $$ = this.owner;
      return this.textAnchorForAxisLabel(!$$.config.axis_rotated, this.getXAxisLabelPosition());
  };
  Axis.prototype.textAnchorForYAxisLabel = function textAnchorForYAxisLabel() {
      var $$ = this.owner;
      return this.textAnchorForAxisLabel($$.config.axis_rotated, this.getYAxisLabelPosition());
  };
  Axis.prototype.textAnchorForY2AxisLabel = function textAnchorForY2AxisLabel() {
      var $$ = this.owner;
      return this.textAnchorForAxisLabel($$.config.axis_rotated, this.getY2AxisLabelPosition());
  };
  Axis.prototype.getMaxTickWidth = function getMaxTickWidth(id, withoutRecompute) {
      var $$ = this.owner, config = $$.config,
          maxWidth = 0, targetsToShow, scale, axis, dummy, svg;
      if (withoutRecompute && $$.currentMaxTickWidths[id]) {
          return $$.currentMaxTickWidths[id];
      }
      if ($$.svg) {
          targetsToShow = $$.filterTargetsToShow($$.data.targets);
          if (id === 'y') {
              scale = $$.y.copy().domain($$.getYDomain(targetsToShow, 'y'));
              axis = this.getYAxis(scale, $$.yOrient, config.axis_y_tick_format, $$.yAxisTickValues, false, true, true);
          } else if (id === 'y2') {
              scale = $$.y2.copy().domain($$.getYDomain(targetsToShow, 'y2'));
              axis = this.getYAxis(scale, $$.y2Orient, config.axis_y2_tick_format, $$.y2AxisTickValues, false, true, true);
          } else {
              scale = $$.x.copy().domain($$.getXDomain(targetsToShow));
              axis = this.getXAxis(scale, $$.xOrient, $$.xAxisTickFormat, $$.xAxisTickValues, false, true, true);
              this.updateXAxisTickValues(targetsToShow, axis);
          }
          dummy = $$.d3.select('body').append('div').classed('c3', true);
          svg = dummy.append("svg").style('visibility', 'hidden').style('position', 'fixed').style('top', 0).style('left', 0),
          svg.append('g').call(axis).each(function () {
              $$.d3.select(this).selectAll('text').each(function () {
                  var box = this.getBoundingClientRect();
                  if (maxWidth < box.width) { maxWidth = box.width; }
              });
              dummy.remove();
          });
      }
      $$.currentMaxTickWidths[id] = maxWidth <= 0 ? $$.currentMaxTickWidths[id] : maxWidth;
      return $$.currentMaxTickWidths[id];
  };
  
  Axis.prototype.updateLabels = function updateLabels(withTransition) {
      var $$ = this.owner;
      var axisXLabel = $$.main.select('.' + CLASS.axisX + ' .' + CLASS.axisXLabel),
          axisYLabel = $$.main.select('.' + CLASS.axisY + ' .' + CLASS.axisYLabel),
          axisY2Label = $$.main.select('.' + CLASS.axisY2 + ' .' + CLASS.axisY2Label);
      (withTransition ? axisXLabel.transition() : axisXLabel)
          .attr("x", this.xForXAxisLabel.bind(this))
          .attr("dx", this.dxForXAxisLabel.bind(this))
          .attr("dy", this.dyForXAxisLabel.bind(this))
          .text(this.textForXAxisLabel.bind(this));
      (withTransition ? axisYLabel.transition() : axisYLabel)
          .attr("x", this.xForYAxisLabel.bind(this))
          .attr("dx", this.dxForYAxisLabel.bind(this))
          .attr("dy", this.dyForYAxisLabel.bind(this))
          .text(this.textForYAxisLabel.bind(this));
      (withTransition ? axisY2Label.transition() : axisY2Label)
          .attr("x", this.xForY2AxisLabel.bind(this))
          .attr("dx", this.dxForY2AxisLabel.bind(this))
          .attr("dy", this.dyForY2AxisLabel.bind(this))
          .text(this.textForY2AxisLabel.bind(this));
  };
  Axis.prototype.getPadding = function getPadding(padding, key, defaultValue, domainLength) {
      var p = typeof padding === 'number' ? padding : padding[key];
      if (!isValue(p)) {
          return defaultValue;
      }
      if (padding.unit === 'ratio') {
          return padding[key] * domainLength;
      }
      // assume padding is pixels if unit is not specified
      return this.convertPixelsToAxisPadding(p, domainLength);
  };
  Axis.prototype.convertPixelsToAxisPadding = function convertPixelsToAxisPadding(pixels, domainLength) {
      var $$ = this.owner,
          length = $$.config.axis_rotated ? $$.width : $$.height;
      return domainLength * (pixels / length);
  };
  Axis.prototype.generateTickValues = function generateTickValues(values, tickCount, forTimeSeries) {
      var tickValues = values, targetCount, start, end, count, interval, i, tickValue;
      if (tickCount) {
          targetCount = isFunction(tickCount) ? tickCount() : tickCount;
          // compute ticks according to tickCount
          if (targetCount === 1) {
              tickValues = [values[0]];
          } else if (targetCount === 2) {
              tickValues = [values[0], values[values.length - 1]];
          } else if (targetCount > 2) {
              count = targetCount - 2;
              start = values[0];
              end = values[values.length - 1];
              interval = (end - start) / (count + 1);
              // re-construct unique values
              tickValues = [start];
              for (i = 0; i < count; i++) {
                  tickValue = +start + interval * (i + 1);
                  tickValues.push(forTimeSeries ? new Date(tickValue) : tickValue);
              }
              tickValues.push(end);
          }
      }
      if (!forTimeSeries) { tickValues = tickValues.sort(function (a, b) { return a - b; }); }
      return tickValues;
  };
  Axis.prototype.generateTransitions = function generateTransitions(duration) {
      var $$ = this.owner, axes = $$.axes;
      return {
          axisX: duration ? axes.x.transition().duration(duration) : axes.x,
          axisY: duration ? axes.y.transition().duration(duration) : axes.y,
          axisY2: duration ? axes.y2.transition().duration(duration) : axes.y2,
          axisSubX: duration ? axes.subx.transition().duration(duration) : axes.subx
      };
  };
  Axis.prototype.redraw = function redraw(transitions, isHidden) {
      var $$ = this.owner;
      $$.axes.x.style("opacity", isHidden ? 0 : 1);
      $$.axes.y.style("opacity", isHidden ? 0 : 1);
      $$.axes.y2.style("opacity", isHidden ? 0 : 1);
      $$.axes.subx.style("opacity", isHidden ? 0 : 1);
      transitions.axisX.call($$.xAxis);
      transitions.axisY.call($$.yAxis);
      transitions.axisY2.call($$.y2Axis);
      transitions.axisSubX.call($$.subXAxis);
  };
  