Callback chain refactoring and performance improvements (#1254)

Author: Marc-Andre-Rivet

Diff for: .circleci/config.yml

@@ -72,7 +72,7 @@ jobs:
   lint-unit-27:
       <<: *lint-unit
       docker:
-        - image: circleci/python:2.7-stretch-node-browsers
+        - image: circleci/python:2.7.18-stretch-node-browsers
           environment:
             PYLINTRC: .pylintrc
             PYVERSION: python27
@@ -122,7 +122,7 @@ jobs:
   build-core-27:
       <<: *build-core
       docker:
-        - image: circleci/python:2.7-stretch-node-browsers
+        - image: circleci/python:2.7.18-stretch-node-browsers
           environment:
             PYVERSION: python27
 
@@ -172,7 +172,7 @@ jobs:
   build-misc-27:
       <<: *build-misc
       docker:
-        - image: circleci/python:2.7-stretch-node-browsers
+        - image: circleci/python:2.7.18-stretch-node-browsers
           environment:
             PYVERSION: python27
 
@@ -372,7 +372,7 @@ jobs:
   test-27:
       <<: *test
       docker:
-        - image: circleci/python:2.7-stretch-node-browsers
+        - image: circleci/python:2.7.18-stretch-node-browsers
           environment:
             PERCY_ENABLE: 0
             PYVERSION: python27

Diff for: CHANGELOG.md

@@ -9,6 +9,7 @@ This project adheres to [Semantic Versioning](http://semver.org/).
 
 ### Changed
 - [#1237](https://github.com/plotly/dash/pull/1237) Closes [#920](https://github.com/plotly/dash/issues/920): Converts hot reload fetch failures into a server status indicator showing whether the latest fetch succeeded or failed. Callback fetch failures still appear as errors but have a clearer message.
+- [#1254](https://github.com/plotly/dash/pull/1254) Modifies the callback chain implementation and improves performance for apps with a lot of components
 
 ### Fixed
 - [#1255](https://github.com/plotly/dash/pull/1255) Hard hot reload targets only the current window, not the top - so if your app is in an iframe you will only reload the app

Diff for: dash-renderer/@Types/modules.d.ts

@@ -0,0 +1,9 @@
+declare module 'cookie' {
+    const value: {
+        parse: (cookie: string) => {
+            _csrf_token: string
+        }
+    };
+
+    export default value;
+}

Diff for: dash-renderer/babel.config.js

@@ -1,11 +1,16 @@
 module.exports = {
     presets: [
+        '@babel/preset-typescript',
         '@babel/preset-env',
         '@babel/preset-react'
     ],
+    plugins: [
+        '@babel/plugin-proposal-class-properties',
+    ],
     env: {
         test: {
             plugins: [
+                '@babel/plugin-proposal-class-properties',
                 '@babel/plugin-transform-modules-commonjs'
             ]
         }

Diff for: dash-renderer/jest.config.js

@@ -85,7 +85,7 @@ module.exports = {
   // notifyMode: "always",
 
   // A preset that is used as a base for Jest's configuration
-  // preset: null,
+  preset: "ts-jest/presets/js-with-babel",
 
   // Run tests from one or more projects
   // projects: null,