Move index.js to web_src and use webpack to pack them (#8598)

* Move index.js to web_src and use webpack

* Fix initHeatMap

* update eslint and move webpack to devDependencies

* update index.js

* add eslint env node

webpack.config.js

@@ -0,0 +1,20 @@
+const path = require('path');
+const TerserPlugin = require('terser-webpack-plugin');
+
+module.exports = {
+  mode: 'production',
+  entry: {
+    index: './web_src/js/index.js',
+  },
+  devtool: 'source-map',
+  output: {
+    path: path.resolve(__dirname, 'public/js'),
+    filename: "[name].js"
+  },
+  optimization: {
+    minimize: true,
+    minimizer: [new TerserPlugin({ 
+        sourceMap: true
+     })],
+  },
+};