resolve frontend fecs problem (PaddlePaddle#123)

* modify overlay and offset chart view interplay problem

* resolve frontend fecs problem

Author: deqingli

frontend/src/histogram/ui/chart.san

@@ -167,8 +167,7 @@ export default {
             series: seriesOption
         };
 
-        var zr1 = this.myChart.getZr();
-        
+        let zr1 = this.myChart.getZr();
         zr1.on('mousemove', function (e) {
             zr1.remove(zrDrawElement.hoverLine);
             zr1.remove(zrDrawElement.tooltip);
@@ -193,7 +192,7 @@ export default {
         grid.top = '42%';
         grid.left = '4%';
         grid.right = '15%';
-        chartData.forEach((dataItem) => {
+        chartData.forEach(function (dataItem) {
             let lineData = [];
             maxStep = Math.max(dataItem.step, maxStep);
             minStep = Math.min(dataItem.step, minStep);
@@ -296,10 +295,10 @@ export default {
         }
 
         zrDrawElement.hoverDots = [];
-        
+
         let zr = ecChart.getZr();
 
-        function removeTooltip(){
+        function removeTooltip() {
             if (zrDrawElement.hoverLine) {
                 zr.remove(zrDrawElement.hoverLine);
                 zr.remove(zrDrawElement.tooltip);
@@ -318,7 +317,7 @@ export default {
             removeTooltip();
             let nearestIndex = findNearestValue(e.offsetX, e.offsetY);
             if (nearestIndex) {
-                let getCoord = function(pt) {
+                let getCoord = function (pt) {
                     return ecChart.convertToPixel('grid', pt);
                 };
                 let gridRect = ecChart.getModel().getComponent('grid', 0).coordinateSystem.getRect();