diff --git a/bin/nyc.js b/bin/nyc.js
index e6a9be883..4b6154db3 100755
--- a/bin/nyc.js
+++ b/bin/nyc.js
@@ -5,7 +5,7 @@ const configUtil = require('../lib/config-util')
 const { cliWrapper, suppressEPIPE } = require('../lib/commands/helpers')
 const foreground = require('foreground-child')
 const resolveFrom = require('resolve-from')
-const NYC = require('../index.js')
+const NYC = require('..')
 
 // parse configuration and command-line arguments;
 // we keep these values in a few different forms,
@@ -32,7 +32,7 @@ async function main () {
   if (!argv.instrument) argv.instrumenter = './lib/instrumenters/noop'
   else argv.instrumenter = './lib/instrumenters/istanbul'
 
-  var nyc = (new NYC(argv))
+  const nyc = (new NYC(argv))
   if (argv.clean) {
     await nyc.reset()
   } else {
diff --git a/index.js b/index.js
index 6d74d0831..107287bb0 100755
--- a/index.js
+++ b/index.js
@@ -36,7 +36,7 @@ if (/self-coverage/.test(__dirname)) {
 }
 
 function coverageFinder () {
-  var coverage = global.__coverage__
+  let coverage = global.__coverage__
   if (typeof __coverage__ === 'object') coverage = __coverage__
   if (!coverage) coverage = global.__coverage__ = {}
   return coverage
@@ -90,9 +90,10 @@ class NYC {
     this.hookRunInThisContext = config.hookRunInThisContext
     this.fakeRequire = null
 
-    this.processInfo = new ProcessInfo(Object.assign({}, config._processInfo, {
+    this.processInfo = new ProcessInfo({
+      ...config._processInfo,
       directory: path.resolve(this.tempDirectory(), 'processinfo')
-    }))
+    })
 
     this.hashCache = {}
   }
@@ -101,7 +102,7 @@ class NYC {
     const opts = {
       salt: Hash.salt(this.config),
       hashData: (input, metadata) => [metadata.filename],
-      filenamePrefix: metadata => path.parse(metadata.filename).name + '-',
+      filenamePrefix: metadata => `${path.parse(metadata.filename).name}-`,
       onHash: (input, metadata, hash) => {
         this.hashCache[metadata.filename] = hash
       },
@@ -109,7 +110,7 @@ class NYC {
       // when running --all we should not load source-file from
       // cache, we want to instead return the fake source.
       disableCache: this._disableCachingTransform(),
-      ext: ext
+      ext
     }
     if (this._eagerInstantiation) {
       opts.transform = this._transformFactory(this.cacheDirectory)
@@ -157,13 +158,13 @@ class NYC {
   }
 
   _readTranspiledSource (filePath) {
-    var source = null
-    var ext = path.extname(filePath)
+    let source = null
+    let ext = path.extname(filePath)
     if (typeof Module._extensions[ext] === 'undefined') {
       ext = '.js'
     }
     Module._extensions[ext]({
-      _compile: function (content, filename) {
+      _compile (content) {
         source = content
       }
     }, filePath)
@@ -194,7 +195,7 @@ class NYC {
   }
 
   async instrumentAllFiles (input, output) {
-    let inputDir = '.' + path.sep
+    let inputDir = `.${path.sep}`
     const visitor = async relFile => {
       const inFile = path.resolve(inputDir, relFile)
       const inCode = await fs.readFile(inFile, 'utf-8')
@@ -270,12 +271,12 @@ class NYC {
     }
   }
 
-  _transformFactory (cacheDir) {
+  _transformFactory () {
     const instrumenter = this.instrumenter()
     let instrumented
 
     return (code, metadata, hash) => {
-      const filename = metadata.filename
+      const { filename } = metadata
       const sourceMap = {}
 
       if (this._sourceMap) {
@@ -287,10 +288,10 @@ class NYC {
 
       try {
         instrumented = instrumenter.instrumentSync(code, filename, sourceMap)
-      } catch (e) {
-        debugLog('failed to instrument ' + filename + ' with error: ' + e.stack)
+      } catch (error) {
+        debugLog(`failed to instrument ${filename} with error: ${error.stack}`)
         if (this.config.exitOnError) {
-          console.error('Failed to instrument ' + filename)
+          console.error(`Failed to instrument ${filename}`)
           process.exit(1)
         } else {
           instrumented = code
@@ -299,9 +300,8 @@ class NYC {
 
       if (this.fakeRequire) {
         return 'function x () {}'
-      } else {
-        return instrumented
       }
+      return instrumented
     }
   }
 
@@ -314,7 +314,7 @@ class NYC {
   _addHook (type) {
     const handleJs = this._handleJs.bind(this)
     const dummyMatcher = () => true // we do all processing in transformer
-    libHook['hook' + type](dummyMatcher, handleJs, { extensions: this.extensions })
+    libHook[`hook${type}`](dummyMatcher, handleJs, { extensions: this.extensions })
   }
 
   _addRequireHooks () {
@@ -360,7 +360,7 @@ class NYC {
     )
   }
 
-  wrap (bin) {
+  wrap () {
     process.env.NYC_PROCESS_ID = this.processInfo.uuid
     // This is a bug with the spawn-wrap method where
     // we cannot force propagation of NYC_PROCESS_ID.
@@ -375,7 +375,7 @@ class NYC {
   }
 
   writeCoverageFile () {
-    var coverage = coverageFinder()
+    const coverage = coverageFinder()
 
     // Remove any files that should be excluded but snuck into the coverage
     Object.keys(coverage).forEach(function (absFile) {
@@ -392,8 +392,8 @@ class NYC {
       }, this)
     }
 
-    var id = this.processInfo.uuid
-    var coverageFilename = path.resolve(this.tempDirectory(), id + '.json')
+    const id = this.processInfo.uuid
+    const coverageFilename = path.resolve(this.tempDirectory(), `${id}.json`)
 
     fs.writeFileSync(
       coverageFilename,
@@ -476,14 +476,14 @@ class NYC {
   }
 
   _checkCoverage (summary, thresholds, file) {
-    Object.keys(thresholds).forEach(function (key) {
-      var coverage = summary[key].pct
+    Object.keys(thresholds).forEach(key => {
+      const coverage = summary[key].pct
       if (coverage < thresholds[key]) {
         process.exitCode = 1
         if (file) {
-          console.error('ERROR: Coverage for ' + key + ' (' + coverage + '%) does not meet threshold (' + thresholds[key] + '%) for ' + file)
+          console.error(`ERROR: Coverage for ${key} (${coverage}%) does not meet threshold (${thresholds[key]}%) for ${file}`)
         } else {
-          console.error('ERROR: Coverage for ' + key + ' (' + coverage + '%) does not meet global threshold (' + thresholds[key] + '%)')
+          console.error(`ERROR: Coverage for ${key} (${coverage}%) does not meet global threshold (${thresholds[key]}%)`)
         }
       }
     })
diff --git a/lib/commands/check-coverage.js b/lib/commands/check-coverage.js
index cc361d16e..2db439344 100644
--- a/lib/commands/check-coverage.js
+++ b/lib/commands/check-coverage.js
@@ -1,13 +1,13 @@
 'use strict'
 
-const NYC = require('../../index.js')
+const NYC = require('../..')
 const { cliWrapper, suppressEPIPE, setupOptions } = require('./helpers.js')
 
 exports.command = 'check-coverage'
 
 exports.describe = 'check whether coverage is within thresholds provided'
 
-exports.builder = function (yargs) {
+exports.builder = (yargs) => {
   yargs
     .demandCommand(0, 0)
     .example('$0 check-coverage --lines 95', "check whether the JSON in nyc's output folder meets the thresholds provided")
diff --git a/lib/commands/instrument.js b/lib/commands/instrument.js
index cabb43775..e8d3c9a29 100644
--- a/lib/commands/instrument.js
+++ b/lib/commands/instrument.js
@@ -1,6 +1,6 @@
 'use strict'
 
-const NYC = require('../../index.js')
+const NYC = require('../..')
 const path = require('path')
 const { promisify } = require('util')
 const resolveFrom = require('resolve-from')
@@ -11,7 +11,7 @@ exports.command = 'instrument <input> [output]'
 
 exports.describe = 'instruments a file or a directory tree and writes the instrumented code to the desired output location'
 
-exports.builder = function (yargs) {
+exports.builder = (yargs) => {
   yargs
     .demandCommand(0, 0)
     .example('$0 instrument ./lib ./output', 'instrument all .js files in ./lib with coverage and output in ./output')
diff --git a/lib/commands/merge.js b/lib/commands/merge.js
index 0aefd11ec..4a361d44f 100644
--- a/lib/commands/merge.js
+++ b/lib/commands/merge.js
@@ -4,13 +4,13 @@ const makeDir = require('make-dir')
 const fs = require('../fs-promises')
 const { cliWrapper, setupOptions } = require('./helpers.js')
 
-const NYC = require('../../index.js')
+const NYC = require('../..')
 
 exports.command = 'merge <input-directory> [output-file]'
 
 exports.describe = 'merge istanbul format coverage output in a given folder'
 
-exports.builder = function (yargs) {
+exports.builder = (yargs) => {
   yargs
     .demandCommand(0, 0)
     .example('$0 merge ./out coverage.json', 'merge together reports in ./out and output as coverage.json')
diff --git a/lib/commands/report.js b/lib/commands/report.js
index 6efb44166..6cb65870b 100644
--- a/lib/commands/report.js
+++ b/lib/commands/report.js
@@ -1,13 +1,13 @@
 'use strict'
 
-const NYC = require('../../index.js')
+const NYC = require('../..')
 const { cliWrapper, suppressEPIPE, setupOptions } = require('./helpers.js')
 
 exports.command = 'report'
 
 exports.describe = 'run coverage report for .nyc_output'
 
-exports.builder = function (yargs) {
+exports.builder = (yargs) => {
   yargs
     .demandCommand(0, 0)
     .example('$0 report --reporter=lcov', 'output an HTML lcov report to ./coverage')
@@ -17,7 +17,7 @@ exports.builder = function (yargs) {
 
 exports.handler = cliWrapper(async argv => {
   process.env.NYC_CWD = process.cwd()
-  var nyc = new NYC(argv)
+  const nyc = new NYC(argv)
   await nyc.report().catch(suppressEPIPE)
   if (argv.checkCoverage) {
     await nyc.checkCoverage({
diff --git a/lib/instrumenters/istanbul.js b/lib/instrumenters/istanbul.js
index 299f9bfea..3bec3146b 100644
--- a/lib/instrumenters/istanbul.js
+++ b/lib/instrumenters/istanbul.js
@@ -18,7 +18,7 @@ function InstrumenterIstanbul (options) {
 
   return {
     instrumentSync (code, filename, { sourceMap, registerMap }) {
-      var instrumented = instrumenter.instrumentSync(code, filename, sourceMap)
+      let instrumented = instrumenter.instrumentSync(code, filename, sourceMap)
       if (instrumented !== code) {
         registerMap()
       }
@@ -26,10 +26,10 @@ function InstrumenterIstanbul (options) {
       // the instrumenter can optionally produce source maps,
       // this is useful for features like remapping stack-traces.
       if (options.produceSourceMap) {
-        var lastSourceMap = instrumenter.lastSourceMap()
+        const lastSourceMap = instrumenter.lastSourceMap()
         /* istanbul ignore else */
         if (lastSourceMap) {
-          instrumented += '\n' + convertSourceMap.fromObject(lastSourceMap).toComment()
+          instrumented += `\n${convertSourceMap.fromObject(lastSourceMap).toComment()}`
         }
       }
 
diff --git a/lib/instrumenters/noop.js b/lib/instrumenters/noop.js
index b0c9f70f9..3d6313bbc 100644
--- a/lib/instrumenters/noop.js
+++ b/lib/instrumenters/noop.js
@@ -4,7 +4,7 @@ function NOOP () {
   const { readInitialCoverage } = require('istanbul-lib-instrument')
 
   return {
-    instrumentSync (code, filename) {
+    instrumentSync (code) {
       const extracted = readInitialCoverage(code)
       if (extracted) {
         this.fileCoverage = extracted.coverageData
diff --git a/lib/process-args.js b/lib/process-args.js
index 60f5e5e5c..09f172f85 100644
--- a/lib/process-args.js
+++ b/lib/process-args.js
@@ -11,8 +11,8 @@ const commands = [
 module.exports = {
   // don't pass arguments that are meant
   // for nyc to the bin being instrumented.
-  hideInstrumenterArgs: function (yargv) {
-    var argv = process.argv.slice(1)
+  hideInstrumenterArgs (yargv) {
+    let argv = process.argv.slice(1)
     argv = argv.slice(argv.indexOf(yargv._[0]))
     if (argv[0][0] === '-') {
       argv.unshift(process.execPath)
@@ -21,12 +21,12 @@ module.exports = {
   },
   // don't pass arguments for the bin being
   // instrumented to nyc.
-  hideInstrumenteeArgs: function () {
-    var argv = process.argv.slice(2)
-    var yargv = Parser(argv)
+  hideInstrumenteeArgs () {
+    let argv = process.argv.slice(2)
+    const yargv = Parser(argv)
     if (!yargv._.length) return argv
-    for (var i = 0, command; (command = yargv._[i]) !== undefined; i++) {
-      if (~commands.indexOf(command)) return argv
+    for (let i = 0, command; (command = yargv._[i]) !== undefined; i++) {
+      if (commands.includes(command)) return argv
     }
 
     // drop all the arguments after the bin being
diff --git a/lib/register-env.js b/lib/register-env.js
index a91ec5c27..088d78dbe 100644
--- a/lib/register-env.js
+++ b/lib/register-env.js
@@ -22,6 +22,6 @@ for (const env of copyAtLoad) {
   }
 }
 
-module.exports = function updateVariable (envName) {
+module.exports = (envName) => {
   envToCopy[envName] = process.env[envName]
 }
diff --git a/lib/source-maps.js b/lib/source-maps.js
index 8a3914cdf..a0c933f3f 100644
--- a/lib/source-maps.js
+++ b/lib/source-maps.js
@@ -66,7 +66,7 @@ class SourceMaps {
           try {
             const mapPath = this.cachedPath(absFile, hash)
             this.loadedMaps[hash] = JSON.parse(await fs.readFile(mapPath, 'utf8'))
-          } catch (e) {
+          } catch (error) {
             // set to false to avoid repeatedly trying to load the map
             this.loadedMaps[hash] = false
           }
diff --git a/lib/wrap.js b/lib/wrap.js
index cf30637f4..5829d2035 100644
--- a/lib/wrap.js
+++ b/lib/wrap.js
@@ -1,6 +1,6 @@
 'use strict'
 
-const NYC = require('../index.js')
+const NYC = require('..')
 
 const config = JSON.parse(
   process.env.NYC_CONFIG ||
@@ -25,4 +25,4 @@ if (process.env.NYC_CONFIG_OVERRIDE) {
   process.env.NYC_CONFIG = JSON.stringify(config)
 }
 
-;(new NYC(config)).wrap()
+(new NYC(config)).wrap()
diff --git a/self-coverage-helper.js b/self-coverage-helper.js
index 2ef7e82e1..6e7cafe7a 100644
--- a/self-coverage-helper.js
+++ b/self-coverage-helper.js
@@ -15,7 +15,7 @@ module.exports = {
     const selfCoverageDir = path.join(__dirname, '.self_coverage')
     mkdirp.sync(selfCoverageDir)
     fs.writeFileSync(
-      path.join(selfCoverageDir, process.pid + '.json'),
+      path.join(selfCoverageDir, `${process.pid}.json`),
       JSON.stringify(coverage),
       'utf-8'
     )
diff --git a/test/add-all-files.js b/test/add-all-files.js
index 636947300..ae9fe2ffb 100644
--- a/test/add-all-files.js
+++ b/test/add-all-files.js
@@ -78,7 +78,7 @@ t.test('transpiles .js files added via addAllFiles', async t => {
   await fs.unlink(needsTranspilePath)
 })
 
-t.test('does not attempt to transpile files when they are excluded', async t => {
+t.test('does not attempt to transpile files when they are excluded', async () => {
   const notNeedTranspilePath = path.join(fixtures, './do-not-need-transpile.do-not-transpile')
   await fs.writeFile(
     notNeedTranspilePath,
diff --git a/test/config-override.js b/test/config-override.js
index b7263ea11..212d5783b 100644
--- a/test/config-override.js
+++ b/test/config-override.js
@@ -10,6 +10,7 @@ t.test('spawn that does config overriding', t => testSuccess(t, {
   args: [
     '--exclude-after-remap=false',
     '--include=conf-override-root.js',
-    process.execPath, 'conf-override-root.js'
+    process.execPath,
+    'conf-override-root.js'
   ]
 }))
diff --git a/test/helpers/reset-state.js b/test/helpers/reset-state.js
index f11c5e8ec..639914d48 100644
--- a/test/helpers/reset-state.js
+++ b/test/helpers/reset-state.js
@@ -8,14 +8,14 @@ const extensions = Object.assign({}, require.extensions) // eslint-disable-line
 const glob = promisify(require('glob'))
 const rimraf = promisify(require('rimraf'))
 
-module.exports = async function () {
+module.exports = async () => {
   // nuke any temporary files created during test runs.
   const files = await glob('test/**/*/{.nyc_output,.cache}')
   await Promise.all(files.map(f => rimraf(f)))
 
   // reset Node's require cache.
   Object.keys(require.cache).forEach((key) => {
-    if (key.indexOf('node_modules') === -1) delete require.cache[key]
+    if (!key.includes('node_modules')) delete require.cache[key]
   })
 
   // reset any custom loaders for extensions, disabling the stack maintained
diff --git a/test/helpers/run-nyc.js b/test/helpers/run-nyc.js
index ca0adcecf..34f27595e 100644
--- a/test/helpers/run-nyc.js
+++ b/test/helpers/run-nyc.js
@@ -34,7 +34,7 @@ function sanitizeString (str, cwd, leavePathSep) {
 async function runNYC ({ args, tempDir, leavePathSep, cwd = fixturesCLI, env = {} }) {
   const runArgs = [nycBin].concat(tempDir ? ['--temp-dir', tempDir] : [], args)
   const { status, stderr, stdout } = await spawn(process.execPath, runArgs, {
-    cwd: cwd,
+    cwd,
     env: {
       ...envPath,
       ...env
diff --git a/test/helpers/temp-dir-setup.js b/test/helpers/temp-dir-setup.js
index df61807e1..7d416f915 100644
--- a/test/helpers/temp-dir-setup.js
+++ b/test/helpers/temp-dir-setup.js
@@ -11,14 +11,14 @@ const mkdtemp = promisify(fs.mkdtemp)
 
 function tempDirSetup (t, testFile) {
   const { dir, name } = path.parse(testFile)
-  const tempDirBase = path.resolve(dir, 'temp-dir-' + name)
+  const tempDirBase = path.resolve(dir, `temp-dir-${name}`)
 
   makeDir.sync(tempDirBase)
 
   // Do not use arrow function for beforeEach
   // or afterEach, they need this from tap.
   t.beforeEach(async function () {
-    this.tempDir = await mkdtemp(tempDirBase + '/')
+    this.tempDir = await mkdtemp(`${tempDirBase}/`)
   })
 
   t.afterEach(function () {
diff --git a/test/issue-190.js b/test/issue-190.js
index 9e844e6af..ae88c12c1 100644
--- a/test/issue-190.js
+++ b/test/issue-190.js
@@ -13,14 +13,14 @@ const fakebin = path.resolve(fixturesCLI, 'fakebin')
 const spawnOptions = {
   cwd: path.resolve(fixturesCLI, 'run-npm-test-recursive'),
   env: {
-    PATH: fakebin + ':' + process.env.PATH
+    PATH: `${fakebin}:${process.env.PATH}`
   }
 }
 
 async function writeFakeNPM (shebang) {
   const targetPath = path.resolve(fakebin, 'npm')
   const source = await fs.readFile(path.resolve(fakebin, 'npm-template.js'))
-  await fs.writeFile(targetPath, '#!' + shebang + '\n' + source)
+  await fs.writeFile(targetPath, `#!${shebang}\n${source}`)
   await fs.chmod(targetPath, 493) // 0o755
 }
 
diff --git a/test/processinfo.js b/test/processinfo.js
index 30290234e..ca66ffc24 100644
--- a/test/processinfo.js
+++ b/test/processinfo.js
@@ -17,11 +17,15 @@ rimraf.sync(resolve(fixturesCLI, tmp))
 t.teardown(() => rimraf(resolve(fixturesCLI, tmp)))
 
 t.test('build some processinfo', t => {
-  var args = [
-    bin, '-t', tmp,
-    node, 'selfspawn-fibonacci.js', '5'
+  const args = [
+    bin,
+    '-t',
+    tmp,
+    node,
+    'selfspawn-fibonacci.js',
+    '5'
   ]
-  var proc = spawn(process.execPath, args, {
+  const proc = spawn(process.execPath, args, {
     cwd: fixturesCLI,
     env: {
       PATH: process.env.PATH,
diff --git a/test/wrap.js b/test/wrap.js
index 2d28c2a2b..bf7d88718 100644
--- a/test/wrap.js
+++ b/test/wrap.js
@@ -28,8 +28,8 @@ t.test('wraps modules with coverage counters when they are required', async t =>
 
 t.test('wraps modules with coverage counters when the custom require hook compiles them', async t => {
   let required = false
-  const hook = function (module, filename) {
-    if (filename.indexOf('check-instrumented.js') !== -1) {
+  const hook = (module, filename) => {
+    if (filename.includes('check-instrumented.js')) {
       required = true
     }
     module._compile(fs.readFileSync(filename, 'utf8'), filename)