Add Babel plugin for optional chaining

babel.config.js

@@ -21,6 +21,7 @@ const plugins = [
   '@babel/plugin-proposal-class-properties',
   '@babel/plugin-proposal-json-strings',
   '@babel/plugin-proposal-private-methods',
+  '@babel/plugin-proposal-optional-chaining',
 ];
 
 // add code coverage tooling if necessary

package.json

@@ -33,6 +33,7 @@
     "@babel/core": "^7.6.2",
     "@babel/plugin-proposal-class-properties": "^7.5.5",
     "@babel/plugin-proposal-json-strings": "^7.2.0",
+    "@babel/plugin-proposal-optional-chaining": "^7.7.5",
     "@babel/plugin-proposal-private-methods": "^7.6.0",
     "@babel/plugin-syntax-dynamic-import": "^7.2.0",
     "@babel/plugin-syntax-import-meta": "^7.2.0",

yarn.lock

@@ -278,6 +278,14 @@
     "@babel/helper-plugin-utils" "^7.0.0"
     "@babel/plugin-syntax-optional-catch-binding" "^7.2.0"
 
+"@babel/plugin-proposal-optional-chaining@^7.7.5":
+  version "7.7.5"
+  resolved "https://registry.yarnpkg.com/@babel/plugin-proposal-optional-chaining/-/plugin-proposal-optional-chaining-7.7.5.tgz#f0835f044cef85b31071a924010a2a390add11d4"
+  integrity sha512-sOwFqT8JSchtJeDD+CjmWCaiFoLxY4Ps7NjvwHC/U7l4e9i5pTRNt8nDMIFSOUL+ncFbYSwruHM8WknYItWdXw==
+  dependencies:
+    "@babel/helper-plugin-utils" "^7.0.0"
+    "@babel/plugin-syntax-optional-chaining" "^7.7.4"
+
 "@babel/plugin-proposal-private-methods@^7.6.0":
   version "7.6.0"
   resolved "https://registry.yarnpkg.com/@babel/plugin-proposal-private-methods/-/plugin-proposal-private-methods-7.6.0.tgz#19ddc493c7b5d47afdd4291e740c609a83c9fae4"
@@ -337,6 +345,13 @@
   dependencies:
     "@babel/helper-plugin-utils" "^7.0.0"
 
+"@babel/plugin-syntax-optional-chaining@^7.7.4":
+  version "7.7.4"
+  resolved "https://registry.yarnpkg.com/@babel/plugin-syntax-optional-chaining/-/plugin-syntax-optional-chaining-7.7.4.tgz#c91fdde6de85d2eb8906daea7b21944c3610c901"
+  integrity sha512-2MqYD5WjZSbJdUagnJvIdSfkb/ucOC9/1fRJxm7GAxY6YQLWlUvkfxoNbUPcPLHJyetKUDQ4+yyuUyAoc0HriA==
+  dependencies:
+    "@babel/helper-plugin-utils" "^7.0.0"
+
 "@babel/plugin-transform-arrow-functions@^7.2.0":
   version "7.2.0"
   resolved "https://registry.yarnpkg.com/@babel/plugin-transform-arrow-functions/-/plugin-transform-arrow-functions-7.2.0.tgz#9aeafbe4d6ffc6563bf8f8372091628f00779550"