Fix some ES6 syntax issue and add support for getting axis keys from …

…options

xAxis and yAxis keys are currently hard-coded as either 'x', or 't' and
'y'.

This change adds support to use the provided xAxisKey and yAxisKey
values from the chartjs options object that is provided by the user.

Fall back to the original behavior in case these are not provided.

This is a non-breaking change.

Also, add the 'const' keyword in front of the addFilter method.

README.md

@@ -38,6 +38,8 @@ To configure the trendline plugin you simply add a new config options to your da
 		colorMax: "green",
 		lineStyle: "dotted|solid",
 		width: 2,
+		xAxisKey: "time" (optional),
+		yAxisKey: "usage" (optional),
 		projection: true|false (optional)
 	}
 }

package.json

@@ -1,6 +1,6 @@
 {
   "name": "chartjs-plugin-trendline",
-  "version": "2.0.5",
+  "version": "2.1.0",
   "description": "Trendline for Chart.js",
   "main": "src/chartjs-plugin-trendline.js",
   "scripts": {

src/chartjs-plugin-trendline.js

@@ -45,32 +45,37 @@ const pluginTrendlineLinear = {
     },
 };
 
-addFitter = (datasetMeta, ctx, dataset, xScale, yScale) => {
+const addFitter = (datasetMeta, ctx, dataset, xScale, yScale) => {
     let defaultColor = dataset.borderColor || 'rgba(169,169,169, .6)';
     let colorMin = dataset.trendlineLinear.colorMin || defaultColor;
     let colorMax = dataset.trendlineLinear.colorMax || defaultColor;
     let lineWidth = dataset.trendlineLinear.width || dataset.borderWidth;
     let lineStyle = dataset.trendlineLinear.lineStyle || 'solid';
     let fillColor = dataset.trendlineLinear.fillColor;
 
+    const parsing = typeof datasetMeta.controller.chart.options.parsing === "object" ?
+        datasetMeta.controller.chart.options.parsing : undefined;
+    const xAxisKey = dataset.trendlineLinear.xAxisKey || parsing ? parsing.xAxisKey : "x";
+    const yAxisKey = dataset.trendlineLinear.yAxisKey || parsing ? parsing.yAxisKey : "y";
+
     lineWidth = lineWidth !== undefined ? lineWidth : 3;
 
     let fitter = new LineFitter();
     let firstIndex = dataset.data.findIndex((d) => {
         return d !== undefined && d !== null;
     });
     let lastIndex = dataset.data.length - 1;
-    let startPos = datasetMeta.data[firstIndex].x;
-    let endPos = datasetMeta.data[lastIndex].x;
+    let startPos = datasetMeta.data[firstIndex][xAxisKey];
+    let endPos = datasetMeta.data[lastIndex][xAxisKey];
     let xy = typeof dataset.data[firstIndex] === 'object';
 
     dataset.data.forEach((data, index) => {
         if (data == null) return;
 
         if (['time', 'timeseries'].includes(xScale.options.type)) {
-            let x = data.x != null ? data.x : data.t;
+            let x = data[xAxisKey] != null ? data[xAxisKey] : data.t;
             if (x !== undefined) {
-                fitter.add(new Date(x).getTime(), data.y);
+                fitter.add(new Date(x).getTime(), data[yAxisKey]);
             } else {
                 fitter.add(index, data);
             }