diff --git a/src/cli/command.js b/src/cli/command.js
index bed84797bab5e..135d03e32b6c1 100644
--- a/src/cli/command.js
+++ b/src/cli/command.js
@@ -82,7 +82,7 @@ Command.prototype.parseOptions = _.wrap(Command.prototype.parseOptions, function
 
 Command.prototype.action = _.wrap(Command.prototype.action, function (action, fn) {
   return action.call(this, function (...args) {
-    var ret = fn.apply(this, args);
+    let ret = fn.apply(this, args);
     if (ret && typeof ret.then === 'function') {
       ret.then(null, function (e) {
         console.log('FATAL CLI ERROR', e.stack);
diff --git a/src/cli/help.js b/src/cli/help.js
index 539b05e0ed033..89bc90a24cbd6 100644
--- a/src/cli/help.js
+++ b/src/cli/help.js
@@ -69,6 +69,6 @@ ${indent(cmd.optionHelp(), 2)}
 }
 
 function humanReadableArgName(arg) {
-  var nameOutput = arg.name + (arg.variadic === true ? '...' : '');
+  let nameOutput = arg.name + (arg.variadic === true ? '...' : '');
   return arg.required ? '<' + nameOutput + '>' : '[' + nameOutput + ']';
 }
diff --git a/src/cli_plugin/cli.js b/src/cli_plugin/cli.js
index 5f322a48bb289..5a09416a9cb1a 100644
--- a/src/cli_plugin/cli.js
+++ b/src/cli_plugin/cli.js
@@ -23,7 +23,7 @@ program
 .command('help <command>')
 .description('get the help for a specific command')
 .action(function (cmdName) {
-  var cmd = _.find(program.commands, { _name: cmdName });
+  let cmd = _.find(program.commands, { _name: cmdName });
   if (!cmd) return program.error(`unknown command ${cmdName}`);
   cmd.help();
 });
@@ -35,7 +35,7 @@ program
 });
 
 // check for no command name
-var subCommand = argv[2] && !String(argv[2][0]).match(/^-|^\.|\//);
+let subCommand = argv[2] && !String(argv[2][0]).match(/^-|^\.|\//);
 if (!subCommand) {
   program.defaultHelp();
 }
diff --git a/src/fixtures/agg_resp/geohash_grid.js b/src/fixtures/agg_resp/geohash_grid.js
index b62d56d21ae57..33a446ff360b2 100644
--- a/src/fixtures/agg_resp/geohash_grid.js
+++ b/src/fixtures/agg_resp/geohash_grid.js
@@ -17,23 +17,23 @@ export default function GeoHashGridAggResponseFixture() {
   //   },
   // });
 
-  var geoHashCharts = _.union(
+  let geoHashCharts = _.union(
     _.range(48, 57), // 0-9
     _.range(65, 90), // A-Z
     _.range(97, 122) // a-z
   );
 
-  var totalDocCount = 0;
+  let totalDocCount = 0;
 
-  var tags = _.times(_.random(4, 20), function (i) {
+  let tags = _.times(_.random(4, 20), function (i) {
     // random number of tags
-    var docCount = 0;
-    var buckets = _.times(_.random(40, 200), function () {
+    let docCount = 0;
+    let buckets = _.times(_.random(40, 200), function () {
       return _.sample(geoHashCharts, 3).join('');
     })
     .sort()
     .map(function (geoHash) {
-      var count = _.random(1, 5000);
+      let count = _.random(1, 5000);
 
       totalDocCount += count;
       docCount += count;
diff --git a/src/fixtures/fake_chart_events.js b/src/fixtures/fake_chart_events.js
index 949234c8c58ec..383a61c900815 100644
--- a/src/fixtures/fake_chart_events.js
+++ b/src/fixtures/fake_chart_events.js
@@ -1,4 +1,4 @@
-var results = {};
+let results = {};
 
 results.timeSeries = {
   data: {
diff --git a/src/fixtures/fake_hierarchical_data.js b/src/fixtures/fake_hierarchical_data.js
index d15ae5253e7be..2b1096cc9c271 100644
--- a/src/fixtures/fake_hierarchical_data.js
+++ b/src/fixtures/fake_hierarchical_data.js
@@ -1,4 +1,4 @@
-var data = {  };
+let data = {  };
 
 data.metricOnly = {
   hits: { total: 1000, hits: [], max_score: 0 },
diff --git a/src/fixtures/fake_row.js b/src/fixtures/fake_row.js
index 837d4081c989c..032fe0f1a9235 100644
--- a/src/fixtures/fake_row.js
+++ b/src/fixtures/fake_row.js
@@ -1,5 +1,5 @@
 import _ from 'lodash';
-var longString = Array(200).join('_');
+let longString = Array(200).join('_');
 
 export default function (id, mapping) {
   function fakeVals(type) {
diff --git a/src/fixtures/logstash_fields.js b/src/fixtures/logstash_fields.js
index c23cfafbbcaf6..e4f993da81470 100644
--- a/src/fixtures/logstash_fields.js
+++ b/src/fixtures/logstash_fields.js
@@ -1,5 +1,5 @@
 function stubbedLogstashFields() {
-  var sourceData = [
+  let sourceData = [
     { name: 'bytes',              type: 'number',     indexed: true,  analyzed: true, sortable:  true,  filterable: true,   count: 10 },
     { name: 'ssl',                type: 'boolean',    indexed: true,  analyzed: true, sortable:  true,  filterable: true,   count: 20 },
     { name: '@timestamp',         type: 'date',       indexed: true,  analyzed: true, sortable:  true,  filterable: true,   count: 30 },
diff --git a/src/fixtures/mock_courier.js b/src/fixtures/mock_courier.js
index d1932a2837e45..ef68696693551 100644
--- a/src/fixtures/mock_courier.js
+++ b/src/fixtures/mock_courier.js
@@ -3,11 +3,11 @@ import sinon from 'auto-release-sinon';
 import FixturesStubbedLogstashIndexPatternProvider from 'fixtures/stubbed_logstash_index_pattern';
 
 export default function (Private, Promise) {
-  var indexPatterns = Private(FixturesStubbedLogstashIndexPatternProvider);
-  var getIndexPatternStub = sinon.stub();
+  let indexPatterns = Private(FixturesStubbedLogstashIndexPatternProvider);
+  let getIndexPatternStub = sinon.stub();
   getIndexPatternStub.returns(Promise.resolve(indexPatterns));
 
-  var courier = {
+  let courier = {
     indexPatterns: { get: getIndexPatternStub },
     getStub: getIndexPatternStub
   };
diff --git a/src/fixtures/mock_ui_state.js b/src/fixtures/mock_ui_state.js
index c4b77a4b8ba5d..50d913ae337e8 100644
--- a/src/fixtures/mock_ui_state.js
+++ b/src/fixtures/mock_ui_state.js
@@ -1,5 +1,5 @@
 import _ from 'lodash';
-var keys = {};
+let keys = {};
 export default {
   get: function (path, def) {
     return keys[path] == null ? def : keys[path];
diff --git a/src/fixtures/stubbed_doc_source_response.js b/src/fixtures/stubbed_doc_source_response.js
index 7034d99427101..5bed6d41af348 100644
--- a/src/fixtures/stubbed_doc_source_response.js
+++ b/src/fixtures/stubbed_doc_source_response.js
@@ -1,7 +1,7 @@
 import FixturesLogstashFieldsProvider from 'fixtures/logstash_fields';
 
 function stubbedDocSourceResponse(Private) {
-  var mockLogstashFields = Private(FixturesLogstashFieldsProvider);
+  let mockLogstashFields = Private(FixturesLogstashFieldsProvider);
 
   return function (id, index) {
     index = index || '.kibana';
diff --git a/src/fixtures/stubbed_logstash_index_pattern.js b/src/fixtures/stubbed_logstash_index_pattern.js
index 1bbcfd76e175c..8377132b6d8ea 100644
--- a/src/fixtures/stubbed_logstash_index_pattern.js
+++ b/src/fixtures/stubbed_logstash_index_pattern.js
@@ -3,21 +3,21 @@ import TestUtilsStubIndexPatternProvider from 'test_utils/stub_index_pattern';
 import IndexPatternsFieldTypesProvider from 'ui/index_patterns/_field_types';
 import FixturesLogstashFieldsProvider from 'fixtures/logstash_fields';
 export default function stubbedLogstashIndexPatternService(Private) {
-  var StubIndexPattern = Private(TestUtilsStubIndexPatternProvider);
-  var fieldTypes = Private(IndexPatternsFieldTypesProvider);
-  var mockLogstashFields = Private(FixturesLogstashFieldsProvider);
+  let StubIndexPattern = Private(TestUtilsStubIndexPatternProvider);
+  let fieldTypes = Private(IndexPatternsFieldTypesProvider);
+  let mockLogstashFields = Private(FixturesLogstashFieldsProvider);
 
 
-  var fields = mockLogstashFields.map(function (field) {
+  let fields = mockLogstashFields.map(function (field) {
     field.displayName = field.name;
-    var type = fieldTypes.byName[field.type];
+    let type = fieldTypes.byName[field.type];
     if (!type) throw new TypeError('unknown type ' + field.type);
     if (!_.has(field, 'sortable')) field.sortable = type.sortable;
     if (!_.has(field, 'filterable')) field.filterable = type.filterable;
     return field;
   });
 
-  var indexPattern = new StubIndexPattern('logstash-*', 'time', fields);
+  let indexPattern = new StubIndexPattern('logstash-*', 'time', fields);
   indexPattern.id = 'logstash-*';
 
   return indexPattern;
diff --git a/src/fixtures/stubbed_search_source.js b/src/fixtures/stubbed_search_source.js
index 3cf015475b750..118aaede15047 100644
--- a/src/fixtures/stubbed_search_source.js
+++ b/src/fixtures/stubbed_search_source.js
@@ -3,8 +3,8 @@ import searchResponse from 'fixtures/search_response';
 import FixturesStubbedLogstashIndexPatternProvider from 'fixtures/stubbed_logstash_index_pattern';
 
 export default function stubSearchSource(Private, $q, Promise) {
-  var deferedResult = $q.defer();
-  var indexPattern = Private(FixturesStubbedLogstashIndexPatternProvider);
+  let deferedResult = $q.defer();
+  let indexPattern = Private(FixturesStubbedLogstashIndexPatternProvider);
 
   return {
     sort: sinon.spy(),
diff --git a/src/fixtures/vislib/_vis_fixture.js b/src/fixtures/vislib/_vis_fixture.js
index 589a65f8a8160..8f06190120053 100644
--- a/src/fixtures/vislib/_vis_fixture.js
+++ b/src/fixtures/vislib/_vis_fixture.js
@@ -2,7 +2,7 @@ import _ from 'lodash';
 import $ from 'jquery';
 import VislibVisProvider from 'ui/vislib/vis';
 
-var $visCanvas = $('<div>')
+let $visCanvas = $('<div>')
   .attr('id', 'vislib-vis-fixtures')
   .css({
     height: '500px',
@@ -15,8 +15,8 @@ var $visCanvas = $('<div>')
   })
   .appendTo('body');
 
-var count = 0;
-var visHeight = $visCanvas.height();
+let count = 0;
+let visHeight = $visCanvas.height();
 
 $visCanvas.new = function () {
   count += 1;
@@ -32,7 +32,7 @@ afterEach(function () {
 
 module.exports = function VislibFixtures(Private) {
   return function (visLibParams) {
-    var Vis = Private(VislibVisProvider);
+    let Vis = Private(VislibVisProvider);
     return new Vis($visCanvas.new(), _.defaults({}, visLibParams || {}, {
       shareYAxis: true,
       addTooltip: true,
diff --git a/src/optimize/babel_options.build.js b/src/optimize/babel_options.build.js
index c58e6bee57f99..885a318ab84d1 100644
--- a/src/optimize/babel_options.build.js
+++ b/src/optimize/babel_options.build.js
@@ -1,5 +1,5 @@
 import { cloneDeep } from 'lodash';
-var fromRoot = require('path').resolve.bind(null, __dirname, '../../');
+let fromRoot = require('path').resolve.bind(null, __dirname, '../../');
 
 if (!process.env.BABEL_CACHE_PATH) {
   process.env.BABEL_CACHE_PATH = fromRoot('optimize/.babelcache.json');
diff --git a/src/optimize/babel_options.js b/src/optimize/babel_options.js
index df98c4b71a811..e562700da3708 100644
--- a/src/optimize/babel_options.js
+++ b/src/optimize/babel_options.js
@@ -1,5 +1,8 @@
-var cloneDeep = require('lodash').cloneDeep;
-var fromRoot = require('path').resolve.bind(null, __dirname, '../../');
+// this file is not transpiled
+'use strict'; // eslint-disable-line strict
+
+let cloneDeep = require('lodash').cloneDeep;
+let fromRoot = require('path').resolve.bind(null, __dirname, '../../');
 
 if (!process.env.BABEL_CACHE_PATH) {
   process.env.BABEL_CACHE_PATH = fromRoot('optimize/.babelcache.json');
diff --git a/src/plugins/kbn_doc_views/public/views/table.js b/src/plugins/kbn_doc_views/public/views/table.js
index c0ebc4b8edf6b..af201f39c3539 100644
--- a/src/plugins/kbn_doc_views/public/views/table.js
+++ b/src/plugins/kbn_doc_views/public/views/table.js
@@ -26,7 +26,7 @@ docViewsRegistry.register(function () {
         };
 
         $scope.showArrayInObjectsWarning = function (row, field) {
-          var value = $scope.flattened[field];
+          let value = $scope.flattened[field];
           return _.isArray(value) && typeof value[0] === 'object';
         };
       }
diff --git a/src/server/config/__tests__/config.js b/src/server/config/__tests__/config.js
index 7a48a7c616572..cf43ce256f585 100644
--- a/src/server/config/__tests__/config.js
+++ b/src/server/config/__tests__/config.js
@@ -9,12 +9,12 @@ import Joi from 'joi';
  *
  * Config should be newed up with a joi schema (containing defaults via joi)
  *
- * var schema = { ... }
+ * let schema = { ... }
  * new Config(schema);
  *
  */
 
-var data = {
+let data = {
   test: {
     hosts: ['host-01', 'host-02'],
     client: {
@@ -25,7 +25,7 @@ var data = {
   }
 };
 
-var schema = Joi.object({
+let schema = Joi.object({
   test: Joi.object({
     enable: Joi.boolean().default(true),
     hosts: Joi.array().items(Joi.string()),
@@ -44,39 +44,39 @@ describe('lib/config/config', function () {
     describe('constructor', function () {
 
       it('should not allow any config if the schema is not passed', function () {
-        var config = new Config();
-        var run = function () {
+        let config = new Config();
+        let run = function () {
           config.set('something.enable', true);
         };
         expect(run).to.throwException();
       });
 
       it('should allow keys in the schema', function () {
-        var config = new Config(schema);
-        var run = function () {
+        let config = new Config(schema);
+        let run = function () {
           config.set('test.client.host', 'http://0.0.0.0');
         };
         expect(run).to.not.throwException();
       });
 
       it('should not allow keys not in the schema', function () {
-        var config = new Config(schema);
-        var run = function () {
+        let config = new Config(schema);
+        let run = function () {
           config.set('paramNotDefinedInTheSchema', true);
         };
         expect(run).to.throwException();
       });
 
       it('should not allow child keys not in the schema', function () {
-        var config = new Config(schema);
-        var run = function () {
+        let config = new Config(schema);
+        let run = function () {
           config.set('test.client.paramNotDefinedInTheSchema', true);
         };
         expect(run).to.throwException();
       });
 
       it('should set defaults', function () {
-        var config = new Config(schema);
+        let config = new Config(schema);
         expect(config.get('test.enable')).to.be(true);
         expect(config.get('test.client.type')).to.be('datastore');
       });
@@ -92,7 +92,7 @@ describe('lib/config/config', function () {
 
       it('should reset the config object with new values', function () {
         config.set(data);
-        var newData = config.get();
+        let newData = config.get();
         newData.test.enable = false;
         config.resetTo(newData);
         expect(config.get()).to.eql(newData);
@@ -134,21 +134,21 @@ describe('lib/config/config', function () {
       });
 
       it('should use an object to set config values', function () {
-        var hosts = ['host-01', 'host-02'];
+        let hosts = ['host-01', 'host-02'];
         config.set({ test: { enable: false, hosts: hosts } });
         expect(config.get('test.enable')).to.be(false);
         expect(config.get('test.hosts')).to.eql(hosts);
       });
 
       it('should use a flatten object to set config values', function () {
-        var hosts = ['host-01', 'host-02'];
+        let hosts = ['host-01', 'host-02'];
         config.set({ 'test.enable': false, 'test.hosts': hosts });
         expect(config.get('test.enable')).to.be(false);
         expect(config.get('test.hosts')).to.eql(hosts);
       });
 
       it('should override values with just the values present', function () {
-        var newData = _.cloneDeep(data);
+        let newData = _.cloneDeep(data);
         config.set(data);
         newData.test.enable = false;
         config.set({ test: { enable: false } });
@@ -156,7 +156,7 @@ describe('lib/config/config', function () {
       });
 
       it('should thow an exception when setting a value with the wrong type', function (done) {
-        var run = function () {
+        let run = function () {
           config.set('test.enable', 'something');
         };
         expect(run).to.throwException(function (err) {
@@ -179,7 +179,7 @@ describe('lib/config/config', function () {
       });
 
       it('should return the whole config object when called without a key', function () {
-        var newData = _.cloneDeep(data);
+        let newData = _.cloneDeep(data);
         newData.test.enable = true;
         expect(config.get()).to.eql(newData);
       });
@@ -194,14 +194,14 @@ describe('lib/config/config', function () {
       });
 
       it('should throw exception for unknown config values', function () {
-        var run = function () {
+        let run = function () {
           config.get('test.does.not.exist');
         };
         expect(run).to.throwException(/Unknown config key: test.does.not.exist/);
       });
 
       it('should not throw exception for undefined known config values', function () {
-        var run = function getUndefValue() {
+        let run = function getUndefValue() {
           config.get('test.undefValue');
         };
         expect(run).to.not.throwException();
@@ -216,13 +216,13 @@ describe('lib/config/config', function () {
       });
 
       it('should allow you to extend the schema at the top level', function () {
-        var newSchema = Joi.object({ test: Joi.boolean().default(true) }).default();
+        let newSchema = Joi.object({ test: Joi.boolean().default(true) }).default();
         config.extendSchema('myTest', newSchema);
         expect(config.get('myTest.test')).to.be(true);
       });
 
       it('should allow you to extend the schema with a prefix', function () {
-        var newSchema = Joi.object({ test: Joi.boolean().default(true) }).default();
+        let newSchema = Joi.object({ test: Joi.boolean().default(true) }).default();
         config.extendSchema('prefix.myTest', newSchema);
         expect(config.get('prefix')).to.eql({ myTest: { test: true }});
         expect(config.get('prefix.myTest')).to.eql({ test: true });
@@ -230,8 +230,8 @@ describe('lib/config/config', function () {
       });
 
       it('should NOT allow you to extend the schema if somethign else is there', function () {
-        var newSchema = Joi.object({ test: Joi.boolean().default(true) }).default();
-        var run = function () {
+        let newSchema = Joi.object({ test: Joi.boolean().default(true) }).default();
+        let run = function () {
           config.extendSchema('test', newSchema);
         };
         expect(run).to.throwException();
@@ -241,7 +241,7 @@ describe('lib/config/config', function () {
 
     describe('#removeSchema(key)', function () {
       it('should completely remove the key', function () {
-        var config = new Config(Joi.object().keys({
+        let config = new Config(Joi.object().keys({
           a: Joi.number().default(1)
         }));
 
@@ -251,7 +251,7 @@ describe('lib/config/config', function () {
       });
 
       it('only removes existing keys', function () {
-        var config = new Config(Joi.object());
+        let config = new Config(Joi.object());
 
         expect(() => config.removeSchema('b')).to.throwException('Unknown schema');
       });
diff --git a/src/server/config/__tests__/explode_by.js b/src/server/config/__tests__/explode_by.js
index 5ca86e331ef11..3514413e575b6 100644
--- a/src/server/config/__tests__/explode_by.js
+++ b/src/server/config/__tests__/explode_by.js
@@ -4,7 +4,7 @@ import expect from 'expect.js';
 describe('explode_by(dot, flatObject)', function () {
 
   it('should explode a flatten object with dots', function () {
-    var flatObject = {
+    let flatObject = {
       'test.enable': true,
       'test.hosts': ['host-01', 'host-02']
     };
@@ -17,7 +17,7 @@ describe('explode_by(dot, flatObject)', function () {
   });
 
   it('should explode a flatten object with slashes', function () {
-    var flatObject = {
+    let flatObject = {
       'test/enable': true,
       'test/hosts': ['host-01', 'host-02']
     };
diff --git a/src/server/config/__tests__/flatten_with.js b/src/server/config/__tests__/flatten_with.js
index 928c441ef4a76..9dc40fc08097e 100644
--- a/src/server/config/__tests__/flatten_with.js
+++ b/src/server/config/__tests__/flatten_with.js
@@ -4,7 +4,7 @@ import expect from 'expect.js';
 describe('flatten_with(dot, nestedObj)', function () {
 
   it('should flatten object with dot', function () {
-    var nestedObj = {
+    let nestedObj = {
       test: {
         enable: true,
         hosts: ['host-01', 'host-02'],
diff --git a/src/server/config/__tests__/override.js b/src/server/config/__tests__/override.js
index 20cb4642a4cb3..18b3117dcbe56 100644
--- a/src/server/config/__tests__/override.js
+++ b/src/server/config/__tests__/override.js
@@ -4,7 +4,7 @@ import expect from 'expect.js';
 describe('override(target, source)', function () {
 
   it('should override the values form source to target', function () {
-    var target = {
+    let target = {
       test: {
         enable: true,
         host: ['host-01', 'host-02'],
@@ -13,7 +13,7 @@ describe('override(target, source)', function () {
         }
       }
     };
-    var source = { test: { client: { type: 'nosql' } } };
+    let source = { test: { client: { type: 'nosql' } } };
     expect(override(target, source)).to.eql({
       test: {
         enable: true,
diff --git a/src/server/config/explode_by.js b/src/server/config/explode_by.js
index 4d9bd0838f356..50e2b2e82615f 100644
--- a/src/server/config/explode_by.js
+++ b/src/server/config/explode_by.js
@@ -1,10 +1,10 @@
 import _ from 'lodash';
 module.exports = function (dot, flatObject) {
-  var fullObject = {};
+  let fullObject = {};
   _.each(flatObject, function (value, key) {
-    var keys = key.split(dot);
+    let keys = key.split(dot);
     (function walk(memo, keys, value) {
-      var _key = keys.shift();
+      let _key = keys.shift();
       if (keys.length === 0) {
         memo[_key] = value;
       } else {
diff --git a/src/server/config/flatten_with.js b/src/server/config/flatten_with.js
index ac4a907130963..d4a276607bfc7 100644
--- a/src/server/config/flatten_with.js
+++ b/src/server/config/flatten_with.js
@@ -1,8 +1,8 @@
 import _ from 'lodash';
 module.exports = function (dot, nestedObj, flattenArrays) {
   let key; // original key
-  var stack = []; // track key stack
-  var flatObj = {};
+  let stack = []; // track key stack
+  let flatObj = {};
   (function flattenObj(obj) {
     _.keys(obj).forEach(function (key) {
       stack.push(key);
diff --git a/src/server/config/override.js b/src/server/config/override.js
index 0a938f29ead3a..ef850a32754ae 100644
--- a/src/server/config/override.js
+++ b/src/server/config/override.js
@@ -3,8 +3,8 @@ import flattenWith from './flatten_with';
 import explodeBy from './explode_by';
 
 module.exports = function (target, source) {
-  var _target = flattenWith('.', target);
-  var _source = flattenWith('.', source);
+  let _target = flattenWith('.', target);
+  let _source = flattenWith('.', source);
   return explodeBy('.', _.defaults(_source, _target));
 };
 
diff --git a/src/server/logging/__tests__/apply_filters_to_keys.js b/src/server/logging/__tests__/apply_filters_to_keys.js
index fc0c520520b47..0175b90ff221b 100644
--- a/src/server/logging/__tests__/apply_filters_to_keys.js
+++ b/src/server/logging/__tests__/apply_filters_to_keys.js
@@ -3,7 +3,7 @@ import expect from 'expect.js';
 
 describe('applyFiltersToKeys(obj, actionsByKey)', function () {
   it('applies for each key+prop in actionsByKey', function () {
-    var data = applyFiltersToKeys({
+    let data = applyFiltersToKeys({
       a: {
         b: {
           c: 1
diff --git a/src/server/logging/apply_filters_to_keys.js b/src/server/logging/apply_filters_to_keys.js
index 860bdd38b76f0..bc85f2fd1f555 100644
--- a/src/server/logging/apply_filters_to_keys.js
+++ b/src/server/logging/apply_filters_to_keys.js
@@ -21,7 +21,7 @@ function apply(obj, key, action) {
           obj[k] = ('' + val).replace(/./g, 'X');
         }
         else if (/\/.+\//.test(action)) {
-          var matches = action.match(/\/(.+)\//);
+          let matches = action.match(/\/(.+)\//);
           if (matches) {
             let regex = new RegExp(matches[1]);
             obj[k] = ('' + val).replace(regex, replacer);
diff --git a/src/server/logging/log_format.js b/src/server/logging/log_format.js
index c1fa7a4744791..7d11c59abd265 100644
--- a/src/server/logging/log_format.js
+++ b/src/server/logging/log_format.js
@@ -41,13 +41,13 @@ module.exports = class TransformObjStream extends Stream.Transform {
   }
 
   _transform(event, enc, next) {
-    var data = this.filter(this.readEvent(event));
+    let data = this.filter(this.readEvent(event));
     this.push(this.format(data) + '\n');
     next();
   }
 
   readEvent(event) {
-    var data = {
+    let data = {
       type: event.event,
       '@timestamp': moment.utc(event.timestamp).format(),
       tags: [].concat(event.tags || []),
@@ -69,7 +69,7 @@ module.exports = class TransformObjStream extends Stream.Transform {
         referer: event.source.referer
       };
 
-      var contentLength = 0;
+      let contentLength = 0;
       if (typeof event.responsePayload === 'object') {
         contentLength = stringify(event.responsePayload).length;
       } else {
@@ -82,7 +82,7 @@ module.exports = class TransformObjStream extends Stream.Transform {
         contentLength: contentLength
       };
 
-      var query = querystring.stringify(event.query);
+      let query = querystring.stringify(event.query);
       if (query) data.req.url += '?' + query;
 
 
diff --git a/src/server/pid/index.js b/src/server/pid/index.js
index 4584d78d81b6b..e43956b959ff2 100644
--- a/src/server/pid/index.js
+++ b/src/server/pid/index.js
@@ -2,19 +2,19 @@ import _ from 'lodash';
 import Boom from 'boom';
 import Promise from 'bluebird';
 import { unlinkSync as unlink } from 'fs';
-var writeFile = Promise.promisify(require('fs').writeFile);
+let writeFile = Promise.promisify(require('fs').writeFile);
 
 module.exports = Promise.method(function (kbnServer, server, config) {
-  var path = config.get('pid.file');
+  let path = config.get('pid.file');
   if (!path) return;
 
-  var pid = String(process.pid);
+  let pid = String(process.pid);
 
   return writeFile(path, pid, { flag: 'wx' })
   .catch(function (err) {
     if (err.code !== 'EEXIST') throw err;
 
-    var log = {
+    let log = {
       tmpl: 'pid file already exists at <%= path %>',
       path: path,
       pid: pid
@@ -36,7 +36,7 @@ module.exports = Promise.method(function (kbnServer, server, config) {
       pid: pid
     });
 
-    var clean = _.once(function (code) {
+    let clean = _.once(function (code) {
       unlink(path);
     });
 
diff --git a/src/server/plugins/scan.js b/src/server/plugins/scan.js
index 07af33f38c98d..baa5147e44530 100644
--- a/src/server/plugins/scan.js
+++ b/src/server/plugins/scan.js
@@ -6,7 +6,7 @@ import { each } from 'bluebird';
 import PluginCollection from './plugin_collection';
 module.exports = async (kbnServer, server, config) => {
 
-  var plugins = kbnServer.plugins = new PluginCollection(kbnServer);
+  let plugins = kbnServer.plugins = new PluginCollection(kbnServer);
 
   let scanDirs = [].concat(config.get('plugins.scanDirs') || []);
   let pluginPaths = [].concat(config.get('plugins.paths') || []);
diff --git a/src/server/status/__tests__/server_status.js b/src/server/status/__tests__/server_status.js
index 82fdeef1675ef..1c18461092fa9 100644
--- a/src/server/status/__tests__/server_status.js
+++ b/src/server/status/__tests__/server_status.js
@@ -17,21 +17,21 @@ describe('ServerStatus class', function () {
 
   describe('#create(name)', function () {
     it('should create a new status by name', function () {
-      var status = serverStatus.create('name');
+      let status = serverStatus.create('name');
       expect(status).to.be.a(Status);
     });
   });
 
   describe('#get(name)', function () {
     it('exposes plugins by name', function () {
-      var status = serverStatus.create('name');
+      let status = serverStatus.create('name');
       expect(serverStatus.get('name')).to.be(status);
     });
   });
 
   describe('#getState(name)', function () {
     it('should expose the state of the plugin by name', function () {
-      var status = serverStatus.create('name');
+      let status = serverStatus.create('name');
       status.green();
       expect(serverStatus.getState('name')).to.be('green');
     });
@@ -39,11 +39,11 @@ describe('ServerStatus class', function () {
 
   describe('#overall()', function () {
     it('considers each status to produce a summary', function () {
-      var status = serverStatus.create('name');
+      let status = serverStatus.create('name');
 
       expect(serverStatus.overall().state).to.be('uninitialized');
 
-      var match = function (overall, state) {
+      let match = function (overall, state) {
         expect(overall).to.have.property('state', state.id);
         expect(overall).to.have.property('title', state.title);
         expect(overall).to.have.property('icon', state.icon);
@@ -65,20 +65,20 @@ describe('ServerStatus class', function () {
 
   describe('#toJSON()', function () {
     it('serializes to overall status and individuals', function () {
-      var one = serverStatus.create('one');
-      var two = serverStatus.create('two');
-      var three = serverStatus.create('three');
+      let one = serverStatus.create('one');
+      let two = serverStatus.create('two');
+      let three = serverStatus.create('three');
 
       one.green();
       two.yellow();
       three.red();
 
-      var obj = JSON.parse(JSON.stringify(serverStatus));
+      let obj = JSON.parse(JSON.stringify(serverStatus));
       expect(obj).to.have.property('overall');
       expect(obj.overall.state).to.eql(serverStatus.overall().state);
       expect(obj.statuses).to.have.length(3);
 
-      var outs = _.indexBy(obj.statuses, 'name');
+      let outs = _.indexBy(obj.statuses, 'name');
       expect(outs.one).to.have.property('state', 'green');
       expect(outs.two).to.have.property('state', 'yellow');
       expect(outs.three).to.have.property('state', 'red');
diff --git a/src/server/status/__tests__/status.js b/src/server/status/__tests__/status.js
index 7f41596db8e76..5d390949cd387 100644
--- a/src/server/status/__tests__/status.js
+++ b/src/server/status/__tests__/status.js
@@ -17,7 +17,7 @@ describe('Status class', function () {
   });
 
   it('emits change when the status is set', function (done) {
-    var status = serverStatus.create('test');
+    let status = serverStatus.create('test');
 
     status.once('change', function (prev, prevMsg) {
       expect(status.state).to.be('green');
@@ -40,8 +40,8 @@ describe('Status class', function () {
   });
 
   it('should only trigger the change listener when something changes', function () {
-    var status = serverStatus.create('test');
-    var stub = sinon.stub();
+    let status = serverStatus.create('test');
+    let stub = sinon.stub();
     status.on('change', stub);
     status.green('Ready');
     status.green('Ready');
@@ -50,17 +50,17 @@ describe('Status class', function () {
   });
 
   it('should create a JSON representation of the status', function () {
-    var status = serverStatus.create('test');
+    let status = serverStatus.create('test');
     status.green('Ready');
 
-    var json = status.toJSON();
+    let json = status.toJSON();
     expect(json.state).to.eql('green');
     expect(json.message).to.eql('Ready');
   });
 
   it('should call on handler if status is already matched', function (done) {
-    var status = serverStatus.create('test');
-    var msg = 'Test Ready';
+    let status = serverStatus.create('test');
+    let msg = 'Test Ready';
     status.green(msg);
 
     status.on('green', function (prev, prevMsg) {
@@ -73,8 +73,8 @@ describe('Status class', function () {
   });
 
   it('should call once handler if status is already matched', function (done) {
-    var status = serverStatus.create('test');
-    var msg = 'Test Ready';
+    let status = serverStatus.create('test');
+    let msg = 'Test Ready';
     status.green(msg);
 
     status.once('green', function (prev, prevMsg) {
@@ -88,16 +88,16 @@ describe('Status class', function () {
 
   function testState(color) {
     it(`should change the state to ${color} when #${color}() is called`, function () {
-      var status = serverStatus.create('test');
-      var message = 'testing ' + color;
+      let status = serverStatus.create('test');
+      let message = 'testing ' + color;
       status[color](message);
       expect(status).to.have.property('state', color);
       expect(status).to.have.property('message', message);
     });
 
     it(`should trigger the "change" listner when #${color}() is called`, function (done) {
-      var status = serverStatus.create('test');
-      var message = 'testing ' + color;
+      let status = serverStatus.create('test');
+      let message = 'testing ' + color;
       status.on('change', function (prev, prevMsg) {
         expect(status.state).to.be(color);
         expect(status.message).to.be(message);
@@ -110,8 +110,8 @@ describe('Status class', function () {
     });
 
     it(`should trigger the "${color}" listner when #${color}() is called`, function (done) {
-      var status = serverStatus.create('test');
-      var message = 'testing ' + color;
+      let status = serverStatus.create('test');
+      let message = 'testing ' + color;
       status.on(color, function (prev, prevMsg) {
         expect(status.state).to.be(color);
         expect(status.message).to.be(message);
diff --git a/src/server/status/index.js b/src/server/status/index.js
index 5efbdf50b7566..fe658f2b35493 100644
--- a/src/server/status/index.js
+++ b/src/server/status/index.js
@@ -22,8 +22,8 @@ module.exports = function (kbnServer, server, config) {
   });
 
   server.decorate('reply', 'renderStatusPage', function () {
-    var app = kbnServer.uiExports.getHiddenApp('status_page');
-    var resp = app ? this.renderApp(app) : this(kbnServer.status.toString());
+    let app = kbnServer.uiExports.getHiddenApp('status_page');
+    let resp = app ? this.renderApp(app) : this(kbnServer.status.toString());
     resp.code(kbnServer.status.isGreen() ? 200 : 503);
     return resp;
   });
diff --git a/src/server/status/metrics.js b/src/server/status/metrics.js
index 52b32af19bfca..b5cfd6784a0f9 100644
--- a/src/server/status/metrics.js
+++ b/src/server/status/metrics.js
@@ -10,7 +10,7 @@ module.exports = function (kbnServer, server, config) {
     let secSinceLast = (now - lastReport) / 1000;
     lastReport = now;
 
-    var port = config.get('server.port');
+    let port = config.get('server.port');
     let requests = _.get(event, ['requests', port, 'total'], 0);
     let requestsPerSecond = requests / secSinceLast;
 
diff --git a/src/server/status/samples.js b/src/server/status/samples.js
index aac5e2efe7bf5..fd2bc4aa27c84 100644
--- a/src/server/status/samples.js
+++ b/src/server/status/samples.js
@@ -7,8 +7,8 @@ function Samples(max) {
 }
 
 Samples.prototype.add = function (sample) {
-  var vals = this.vals;
-  var length = this.length = Math.min(this.length + 1, this.max);
+  let vals = this.vals;
+  let length = this.length = Math.min(this.length + 1, this.max);
 
   _.forOwn(sample, function (val, name) {
     if (val == null) val = null;
diff --git a/src/server/status/server_status.js b/src/server/status/server_status.js
index 4fb914ca00980..33b9e848d8186 100644
--- a/src/server/status/server_status.js
+++ b/src/server/status/server_status.js
@@ -31,15 +31,15 @@ module.exports = class ServerStatus {
   }
 
   overall() {
-    var state = _(this._created)
+    let state = _(this._created)
     .map(function (status) {
       return states.get(status.state);
     })
     .sortBy('severity')
     .pop();
 
-    var statuses = _.where(this._created, { state: state.id });
-    var since = _.get(_.sortBy(statuses, 'since'), [0, 'since']);
+    let statuses = _.where(this._created, { state: state.id });
+    let since = _.get(_.sortBy(statuses, 'since'), [0, 'since']);
 
     return {
       state: state.id,
@@ -59,7 +59,7 @@ module.exports = class ServerStatus {
   }
 
   toString() {
-    var overall = this.overall();
+    let overall = this.overall();
     return `${overall.title} – ${overall.nickname}`;
   }
 
diff --git a/src/server/status/status.js b/src/server/status/status.js
index 929118d08512f..b260694b1cdf2 100644
--- a/src/server/status/status.js
+++ b/src/server/status/status.js
@@ -13,7 +13,7 @@ class Status extends EventEmitter {
 
     this.on('change', function (previous, previousMsg) {
       this.since = new Date();
-      var tags = ['status', name];
+      let tags = ['status', name];
       tags.push(this.state === 'red' ? 'error' : 'info');
 
       server.log(tags, {
diff --git a/src/test_utils/no_digest_promises.js b/src/test_utils/no_digest_promises.js
index 98ce02c45942a..38a4203ab1b45 100644
--- a/src/test_utils/no_digest_promises.js
+++ b/src/test_utils/no_digest_promises.js
@@ -8,7 +8,7 @@ Bluebird.longStackTraces();
  * replace the Promise service with Bluebird so that tests
  * can use promises without having to call $rootScope.apply()
  *
- * var noDigestPromises = require('test_utils/no_digest_promises');
+ * let noDigestPromises = require('test_utils/no_digest_promises');
  *
  * describe('some module that does complex shit with promises', function () {
  *   beforeEach(noDigestPromises.activate);
@@ -16,7 +16,7 @@ Bluebird.longStackTraces();
  * });
  */
 
-var active = false;
+let active = false;
 
 uiModules
 .get('kibana')
diff --git a/src/test_utils/simulate_keys.js b/src/test_utils/simulate_keys.js
index 0eb8c5d7a79b3..8282d8e5cc9e3 100644
--- a/src/test_utils/simulate_keys.js
+++ b/src/test_utils/simulate_keys.js
@@ -2,8 +2,8 @@ import $ from 'jquery';
 import _ from 'lodash';
 import Promise from 'bluebird';
 import keyMap from 'ui/utils/key_map';
-var reverseKeyMap = _.mapValues(_.invert(keyMap), _.ary(_.parseInt, 1));
-var KeyboardEvent = window.KeyboardEvent;
+let reverseKeyMap = _.mapValues(_.invert(keyMap), _.ary(_.parseInt, 1));
+let KeyboardEvent = window.KeyboardEvent;
 
 /**
  * Simulate keyboard events in an element. This allows testing the way that
@@ -35,7 +35,7 @@ var KeyboardEvent = window.KeyboardEvent;
  * @async
  */
 export default function ($el, sequence) {
-  var modifierState = {
+  let modifierState = {
     ctrlKey: false,
     shiftKey: false,
     altKey: false,
@@ -45,7 +45,7 @@ export default function ($el, sequence) {
   return doList(_.clone(sequence));
 
   function setModifier(key, state) {
-    var name = key + 'Key';
+    let name = key + 'Key';
     if (modifierState.hasOwnProperty(name)) {
       modifierState[name] = !!state;
     }
@@ -55,7 +55,7 @@ export default function ($el, sequence) {
     return Promise.try(function () {
       if (!list || !list.length) return;
 
-      var event = list[0];
+      let event = list[0];
       if (_.isString(event)) {
         event = { type: 'press', key: event };
       }
@@ -91,14 +91,14 @@ export default function ($el, sequence) {
   }
 
   function fire(type, key, repeat) {
-    var keyCode = reverseKeyMap[key];
+    let keyCode = reverseKeyMap[key];
     if (!keyCode) throw new TypeError('invalid key "' + key + '"');
 
     if (type === 'keydown') setModifier(key, true);
     if (type === 'keyup') setModifier(key, false);
 
-    var $target = _.isFunction($el) ? $el() : $el;
-    var $event = new $.Event(type, _.defaults({ keyCode: keyCode }, modifierState));
+    let $target = _.isFunction($el) ? $el() : $el;
+    let $event = new $.Event(type, _.defaults({ keyCode: keyCode }, modifierState));
     $target.trigger($event);
   }
 };
diff --git a/src/test_utils/stub_index_pattern.js b/src/test_utils/stub_index_pattern.js
index 7d5f2624c15c0..45938e4acba06 100644
--- a/src/test_utils/stub_index_pattern.js
+++ b/src/test_utils/stub_index_pattern.js
@@ -9,10 +9,10 @@ import RegistryFieldFormatsProvider from 'ui/registry/field_formats';
 import IndexPatternsFlattenHitProvider from 'ui/index_patterns/_flatten_hit';
 import IndexPatternsFieldProvider from 'ui/index_patterns/_field';
 export default function (Private) {
-  var fieldFormats = Private(RegistryFieldFormatsProvider);
-  var flattenHit = Private(IndexPatternsFlattenHitProvider);
+  let fieldFormats = Private(RegistryFieldFormatsProvider);
+  let flattenHit = Private(IndexPatternsFlattenHitProvider);
 
-  var Field = Private(IndexPatternsFieldProvider);
+  let Field = Private(IndexPatternsFieldProvider);
 
   function StubIndexPattern(pattern, timeField, fields) {
     this.id = pattern;
diff --git a/src/utils/package_json.js b/src/utils/package_json.js
index d85a159ddff17..36a953d4c000b 100644
--- a/src/utils/package_json.js
+++ b/src/utils/package_json.js
@@ -5,7 +5,7 @@ let packageDir;
 let packagePath;
 
 while (!packagePath || !existsSync(packagePath)) {
-  var prev = packageDir;
+  let prev = packageDir;
   packageDir = prev ? join(prev, '..') : __dirname;
   packagePath = join(packageDir, 'package.json');