chore: upgrade to eslint@8 (elastic#3409)

We have turned *off* the "no-var" rule that was added to
the "standard" config with this upgrade. See .eslintrc.json
for justification. We are applying "no-var" in examples/...

Using eslint@8 bumps the min node for linting to 12.20.0.

Co-authored-by: Trent Mick <trent.mick@elastic.co>

Author: 2 people

.eslintrc.json

@@ -8,7 +8,16 @@
     "license-header"
   ],
   "rules": {
-    "license-header/header": [ "error", "./dev-utils/license-header.js" ]
+    "license-header/header": ["error", "./dev-utils/license-header.js"],
+    // Regarding "no-var": The opinion of this repository's maintainers is that
+    // while const/let are useful, the use of `var` is not bad and therefore
+    // does not need to be ruled out. Eliminating the use of `var` would be a
+    // large diff that (a) could theoretically cause bugs due to lexical scoping
+    // changes and (b) could theoretically impact perf (e.g. see
+    // https://github.com/microsoft/TypeScript/issues/52924). New code MAY
+    // prefer const/let over `var`. Code in "examples/" MUST use const/let --
+    // this is enforced by "examples/.eslintrc.json".
+    "no-var": "off"
   },
   "ignorePatterns": [
     "/*.example.js", // a pattern for uncommited local dev files to avoid linting

dev-utils/bitrot.js

@@ -136,7 +136,7 @@ function loadSupportedDoc () {
   var state = null // null | 'thead' | 'tbody'
   html.split(/\n/g).forEach(function (line) {
     if (!line.startsWith('|')) {
-
+      // no op
     } else if (state === null) {
       if (line.startsWith('|===')) {
         state = 'thead'
@@ -181,7 +181,7 @@ function loadSupportedDoc () {
   let match
   rows.forEach(function (row) {
     if (row[1] === 'N/A') {
-
+      // skip
     } else if (row[0].includes('<<')) {
       match = /^\s*<<([\w-]+),(.*?)>>/.exec(row[0])
       if (!match) {

examples/.eslintrc.json

@@ -0,0 +1,5 @@
+{
+  "rules": {
+    "no-var": ["error"]
+  }
+}

examples/trace-graphql.js

@@ -10,18 +10,18 @@
 const apm = require('../').start({ // elastic-apm-node
   serviceName: 'example-trace-graphql'
 })
-var { graphql, buildSchema } = require('graphql')
+const { graphql, buildSchema } = require('graphql')
 
 // Construct a schema, using GraphQL schema language
-var schema = buildSchema(`
+const schema = buildSchema(`
   type Query {
     hello: String
     bye: String
   }
 `)
 
 // The root provides a resolver function for each API endpoint
-var root = {
+const root = {
   hello: () => {
     return 'Hello world!'
   },

examples/trace-handlebars.js

@@ -21,7 +21,7 @@ const handlebars = require('handlebars')
 // https://www.elastic.co/guide/en/apm/agent/nodejs/current/custom-transactions.html
 const t1 = apm.startTransaction('t1')
 
-var template = handlebars.compile('Hello, {{name}}!')
+const template = handlebars.compile('Hello, {{name}}!')
 console.log(template({ name: 'world' }))
 console.log(template({ name: 'Bob' }))
 

examples/trace-pg.js

@@ -43,7 +43,7 @@ client.query('SELECT $1::text as message', ['bye'], (err, res) => {
 
 // 2. Using streaming style, i.e. using a `Submittable` as node-postgres calls it.
 const t2 = apm.startTransaction('t2')
-var q = client.query(new Query('select 1 + 1 as solution'))
+const q = client.query(new Query('select 1 + 1 as solution'))
 q.on('error', (err) => {
   console.log('[t2] Failure: err is', err)
   t2.end()

examples/trace-pug.js

@@ -21,7 +21,7 @@ const pug = require('pug')
 // https://www.elastic.co/guide/en/apm/agent/nodejs/current/custom-transactions.html
 const t1 = apm.startTransaction('t1')
 
-var template = pug.compile('p Hello, #{name}!')
+const template = pug.compile('p Hello, #{name}!')
 console.log(template({ name: 'world' }))
 console.log(template({ name: 'Bob' }))
 

examples/trace-tedious.js

@@ -65,7 +65,7 @@ const conn2 = new tedious.Connection(connOpts)
 conn2.on('connect', onConnect2)
 conn2.connect()
 function onConnect2 () {
-  var req = new tedious.Request("select @mynum=42, @mystr='qaz'", function (err, rowCount) {
+  const req = new tedious.Request("select @mynum=42, @mystr='qaz'", function (err, rowCount) {
     console.log('select @mynum ...: err=%s rowCount=%s', err && err.message, rowCount)
     conn2.close()
   })

examples/trace-ws.js

@@ -20,8 +20,8 @@ const apm = require('../').start({ // elastic-apm-node
   serviceName: 'example-trace-ws'
 })
 
-var WebSocket = require('ws')
-var PORT = 4567
+const WebSocket = require('ws')
+const PORT = 4567
 
 // Server
 const wss = new WebSocket.Server({ port: PORT })

lib/instrumentation/modules/elasticsearch.js

@@ -29,7 +29,8 @@ function getTargetUrlFromTransportConfig (config) {
   }
 
   let firstTransportHost = Array.isArray(transportHosts)
-    ? transportHosts[0] : transportHosts
+    ? transportHosts[0]
+    : transportHosts
   if (!firstTransportHost) {
     return null
   }