minor fix

public/app/plugins/datasource/prometheus/datasource.ts

@@ -585,7 +585,7 @@ export class PrometheusDatasource {
   }
 
   getTimeRange(): { start: number; end: number } {
-    let range = this.timeSrv.timeRange();
+    const range = this.timeSrv.timeRange();
     return {
       start: this.getPrometheusTime(range.from, false),
       end: this.getPrometheusTime(range.to, true),

public/app/plugins/datasource/prometheus/specs/datasource.test.ts

@@ -619,9 +619,9 @@ describe('PrometheusDatasource', () => {
       beforeEach(async () => {
         options.annotation.useValueForTime = false;
         backendSrv.datasourceRequest = jest.fn(() => Promise.resolve(response));
-        ctx.ds = new PrometheusDatasource(instanceSettings, q, <any>backendSrv, templateSrv, timeSrv);
+        ctx.ds = new PrometheusDatasource(instanceSettings, q, backendSrv as any, templateSrv, timeSrv);
 
-        await ctx.ds.annotationQuery(options).then(function (data) {
+        await ctx.ds.annotationQuery(options).then(data => {
           results = data;
         });
       });
@@ -639,9 +639,9 @@ describe('PrometheusDatasource', () => {
       beforeEach(async () => {
         options.annotation.useValueForTime = true;
         backendSrv.datasourceRequest = jest.fn(() => Promise.resolve(response));
-        ctx.ds = new PrometheusDatasource(instanceSettings, q, <any>backendSrv, templateSrv, timeSrv);
+        ctx.ds = new PrometheusDatasource(instanceSettings, q, backendSrv as any, templateSrv, timeSrv);
 
-        await ctx.ds.annotationQuery(options).then(function (data) {
+        await ctx.ds.annotationQuery(options).then(data => {
           results = data;
         });
       });