Moved xRange call

`xRange` is only used within the `on('click`)` callback, so doesn't need to be initialised until a click event happens. Also, we need to only check whether the x-axis is date axis if we actually have an x-axis
finos · texodus · May 13, 2019 · Apr 8, 2019 · Apr 9, 2019 · Apr 9, 2019
commit 1b802624db3a12b905c979de90a10aa13188d2d2
diff --git a/packages/perspective-viewer-d3fc/src/js/zoom/zoomableChart.js b/packages/perspective-viewer-d3fc/src/js/zoom/zoomableChart.js
@@ -23,8 +23,8 @@ export default () => {
 
     function zoomableChart(selection) {
         const chartPlotArea = `d3fc-${canvas ? "canvas" : "svg"}.plot-area`;
-        const dateAxis = xCopy.domain()[0] instanceof Date;
         if (xScale || yScale) {
+            const dateAxis = xCopy && xCopy.domain()[0] instanceof Date;
             const zoom = d3.zoom().on("zoom", () => {
                 const {transform} = d3.event;
                 settings.zoom = {
@@ -41,14 +41,14 @@ export default () => {
                 const zoomControls = getZoomControls(selection).style("display", noZoom ? "none" : "");
                 zoomControls.select("#zoom-reset").on("click", () => selection.select(chartPlotArea).call(zoom.transform, d3.zoomIdentity));
 
-                const xRange = xCopy.range();
                 const oneYear = zoomControls.select("#one-year").style("display", dateAxis ? "" : "none");
                 if (dateAxis) {
                     oneYear.on("click", () => {
                         const start = new Date(xScale.domain()[0]);
                         const end = new Date(start);
                         end.setYear(start.getFullYear() + 1);
 
+                        const xRange = xCopy.range();
                         const k = (xRange[1] - xRange[0]) / (xCopy(end) - xCopy(start));
                         const x = -xCopy(start) * k;
                         let y = 0;