Merge branch 'dev' into 4.0

# Conflicts:
#	CHANGELOG.md
#	dist/logger.js
#	dist/vuex.common.js
#	dist/vuex.esm.browser.js
#	dist/vuex.esm.browser.min.js
#	dist/vuex.esm.js
#	dist/vuex.js
#	dist/vuex.min.js
#	package.json
#	test/e2e/cart.spec.js
#	test/e2e/chat.spec.js
#	test/e2e/counter.spec.js
#	test/e2e/todomvc.spec.js
#	test/helpers.js
#	yarn.lock

Author: kiaking

dist/logger.js

@@ -0,0 +1,155 @@
+/*!
+ * vuex v3.4.0
+ * (c) 2020 Evan You
+ * @license MIT
+ */
+(function (global, factory) {
+  typeof exports === 'object' && typeof module !== 'undefined' ? module.exports = factory() :
+  typeof define === 'function' && define.amd ? define(factory) :
+  (global = global || self, global.Vuex = factory());
+}(this, (function () { 'use strict';
+
+  /**
+   * Get the first item that pass the test
+   * by second argument function
+   *
+   * @param {Array} list
+   * @param {Function} f
+   * @return {*}
+   */
+  function find (list, f) {
+    return list.filter(f)[0]
+  }
+
+  /**
+   * Deep copy the given object considering circular structure.
+   * This function caches all nested objects and its copies.
+   * If it detects circular structure, use cached copy to avoid infinite loop.
+   *
+   * @param {*} obj
+   * @param {Array<Object>} cache
+   * @return {*}
+   */
+  function deepCopy (obj, cache) {
+    if ( cache === void 0 ) cache = [];
+
+    // just return if obj is immutable value
+    if (obj === null || typeof obj !== 'object') {
+      return obj
+    }
+
+    // if obj is hit, it is in circular structure
+    var hit = find(cache, function (c) { return c.original === obj; });
+    if (hit) {
+      return hit.copy
+    }
+
+    var copy = Array.isArray(obj) ? [] : {};
+    // put the copy into cache at first
+    // because we want to refer it in recursive deepCopy
+    cache.push({
+      original: obj,
+      copy: copy
+    });
+
+    Object.keys(obj).forEach(function (key) {
+      copy[key] = deepCopy(obj[key], cache);
+    });
+
+    return copy
+  }
+
+  // Credits: borrowed code from fcomb/redux-logger
+
+  function createLogger (ref) {
+    if ( ref === void 0 ) ref = {};
+    var collapsed = ref.collapsed; if ( collapsed === void 0 ) collapsed = true;
+    var filter = ref.filter; if ( filter === void 0 ) filter = function (mutation, stateBefore, stateAfter) { return true; };
+    var transformer = ref.transformer; if ( transformer === void 0 ) transformer = function (state) { return state; };
+    var mutationTransformer = ref.mutationTransformer; if ( mutationTransformer === void 0 ) mutationTransformer = function (mut) { return mut; };
+    var actionFilter = ref.actionFilter; if ( actionFilter === void 0 ) actionFilter = function (action, state) { return true; };
+    var actionTransformer = ref.actionTransformer; if ( actionTransformer === void 0 ) actionTransformer = function (act) { return act; };
+    var logMutations = ref.logMutations; if ( logMutations === void 0 ) logMutations = true;
+    var logActions = ref.logActions; if ( logActions === void 0 ) logActions = true;
+    var logger = ref.logger; if ( logger === void 0 ) logger = console;
+
+    return function (store) {
+      var prevState = deepCopy(store.state);
+
+      if (typeof logger === 'undefined') {
+        return
+      }
+
+      if (logMutations) {
+        store.subscribe(function (mutation, state) {
+          var nextState = deepCopy(state);
+
+          if (filter(mutation, prevState, nextState)) {
+            var formattedTime = getFormattedTime();
+            var formattedMutation = mutationTransformer(mutation);
+            var message = "mutation " + (mutation.type) + formattedTime;
+
+            startMessage(logger, message, collapsed);
+            logger.log('%c prev state', 'color: #9E9E9E; font-weight: bold', transformer(prevState));
+            logger.log('%c mutation', 'color: #03A9F4; font-weight: bold', formattedMutation);
+            logger.log('%c next state', 'color: #4CAF50; font-weight: bold', transformer(nextState));
+            endMessage(logger);
+          }
+
+          prevState = nextState;
+        });
+      }
+
+      if (logActions) {
+        store.subscribeAction(function (action, state) {
+          if (actionFilter(action, state)) {
+            var formattedTime = getFormattedTime();
+            var formattedAction = actionTransformer(action);
+            var message = "action " + (action.type) + formattedTime;
+
+            startMessage(logger, message, collapsed);
+            logger.log('%c action', 'color: #03A9F4; font-weight: bold', formattedAction);
+            endMessage(logger);
+          }
+        });
+      }
+    }
+  }
+
+  function startMessage (logger, message, collapsed) {
+    var startMessage = collapsed
+      ? logger.groupCollapsed
+      : logger.group;
+
+    // render
+    try {
+      startMessage.call(logger, message);
+    } catch (e) {
+      logger.log(message);
+    }
+  }
+
+  function endMessage (logger) {
+    try {
+      logger.groupEnd();
+    } catch (e) {
+      logger.log('—— log end ——');
+    }
+  }
+
+  function getFormattedTime () {
+    var time = new Date();
+    return (" @ " + (pad(time.getHours(), 2)) + ":" + (pad(time.getMinutes(), 2)) + ":" + (pad(time.getSeconds(), 2)) + "." + (pad(time.getMilliseconds(), 3)))
+  }
+
+  function repeat (str, times) {
+    return (new Array(times + 1)).join(str)
+  }
+
+  function pad (num, maxLength) {
+    return repeat('0', maxLength - num.toString().length) + num
+  }
+
+  return createLogger;
+
+})));