frontend: Use backend url from env during build

.taskcluster.yml

@@ -41,6 +41,14 @@ tasks:
         else: ${event.ref[11:]}
       else: 'dev'
 
+    backend_url:
+      $if: 'tasks_for == "github-push"'
+      then:
+        $if: 'event.ref == "refs/heads/testing"'
+        then: 'https://api.coverage.testing.moz.tools'
+        else: 'https://api.coverage.moz.tools'
+      else: 'https://api.coverage.moz.tools'
+
     taskboot_image: "mozilla/taskboot:0.1.9"
   in:
     - taskId: {$eval: as_slugid("check_lint")}
@@ -226,6 +234,8 @@ tasks:
       payload:
         maxRunTime: 3600
         image: node
+        env:
+          BACKEND_URL: "${backend_url}"
         command:
           - sh
           - -lxce

frontend/src/common.js

@@ -36,7 +36,7 @@ export async function main(load, display, opts) {
 
 // Coverage retrieval.
 
-const COVERAGE_BACKEND_HOST = 'https://api.coverage.moz.tools';
+const COVERAGE_BACKEND_HOST = process.env.BACKEND_URL;
 
 function cache_get(cache, key) {
   if (key in cache) {

frontend/webpack.common.js

@@ -1,4 +1,5 @@
 const path = require('path');
+const webpack = require('webpack');
 const { CleanWebpackPlugin } = require('clean-webpack-plugin');
 const HtmlWebpackPlugin = require('html-webpack-plugin')
 const MiniCssExtractPlugin = require('mini-css-extract-plugin');
@@ -18,6 +19,9 @@ module.exports = {
     new MiniCssExtractPlugin({
       filename: 'coverage-[hash].css',
     }),
+    new webpack.EnvironmentPlugin({
+      BACKEND_URL: 'http://localhost:8000',
+    }),
   ],
   module: {
     rules: [