chore(eslint): remove unused expressions (#11041)

* Enable no-unused-expressions ESLint rule
* Fix experimentalObjectRestSpread deprecation error

Author: DanielRuf

.eslintrc.json

@@ -34,6 +34,12 @@
       "as-needed",
       { "requireReturnForObjectLiteral": true }
     ],
+    "no-unused-expressions": [
+      "error",
+      {
+        "allowTaggedTemplates": true
+      }
+    ],
     "consistent-return": ["error"],
     "no-console": "off",
     "no-inner-declarations": "off",

e2e-tests/production-runtime/scripts/chunks.js

@@ -122,7 +122,7 @@ const restore = () => {
 
   console.log(`Restored resources`)
 }
-
+// eslint-disable-next-line no-unused-expressions
 yargs
   .command(
     `block <chunk>`,

packages/gatsby-image/src/index.js

@@ -208,7 +208,10 @@ class Image extends React.Component {
     if (this.state.seenBefore) {
       this.setState({ fadeIn: false })
     }
-    this.props.onLoad && this.props.onLoad()
+
+    if (this.props.onLoad) {
+      this.props.onLoad()
+    }
   }
 
   render() {

packages/gatsby-link/src/index.js

@@ -66,7 +66,9 @@ class GatsbyLink extends React.Component {
   }
 
   handleRef(ref) {
-    this.props.innerRef && this.props.innerRef(ref)
+    if (this.props.innerRef) {
+      this.props.innerRef(ref)
+    }
 
     if (this.state.IOSupported && ref) {
       // If IO supported and element reference found, setup Observer functionality
@@ -120,13 +122,15 @@ class GatsbyLink extends React.Component {
         getProps={getProps}
         innerRef={this.handleRef}
         onMouseEnter={e => {
-          // eslint-disable-line
-          onMouseEnter && onMouseEnter(e)
+          if (onMouseEnter) {
+            onMouseEnter(e)
+          }
           ___loader.hovering(parsePath(to).pathname)
         }}
         onClick={e => {
-          // eslint-disable-line
-          onClick && onClick(e)
+          if (onClick) {
+            onClick(e)
+          }
 
           if (
             e.button === 0 && // ignore right clicks

packages/gatsby-plugin-jss/src/gatsby-browser.js

@@ -4,7 +4,9 @@ const ThemeProvider = require(`react-jss`).ThemeProvider
 // remove the JSS style tag generated on the server to avoid conflicts with the one added on the client
 exports.onInitialClientRender = () => {
   const ssStyles = window.document.getElementById(`server-side-jss`)
-  ssStyles && ssStyles.parentNode.removeChild(ssStyles)
+  if (ssStyles) {
+    ssStyles.parentNode.removeChild(ssStyles)
+  }
 }
 // eslint-disable-next-line react/prop-types
 exports.wrapRootElement = ({ element }, options) => {

packages/gatsby-plugin-react-css-modules/src/gatsby-node.js

@@ -1,7 +1,9 @@
 exports.onCreateBabelConfig = ({ actions }, pluginOptions) => {
   const isDevelopment = process.env.NODE_ENV !== `production`
 
-  pluginOptions.plugins && delete pluginOptions.plugins
+  if (pluginOptions.plugins) {
+    delete pluginOptions.plugins
+  }
 
   actions.setBabelPlugin({
     name: `babel-plugin-react-css-modules`,

packages/gatsby-remark-prismjs/src/highlight-code.js

@@ -30,9 +30,9 @@ module.exports = (language, code, lineNumbersHighlight = []) => {
   // Don't add back the new line character after highlighted lines
   // as they need to be display: block and full-width.
   codeSplits.forEach((split, idx) => {
-    split.highlight
-      ? (finalCode += split.code)
-      : (finalCode += `${split.code}${idx == lastIdx ? `` : `\n`}`)
+    finalCode += split.highlight
+      ? split.code
+      : `${split.code}${idx == lastIdx ? `` : `\n`}`
   })
 
   return finalCode

packages/gatsby-source-contentful/src/gatsby-node.js

@@ -165,7 +165,6 @@ exports.sourceNodes = async (
 
   // Update existing entry nodes that weren't updated but that need reverse
   // links added.
-  Object.keys(foreignReferenceMap)
   existingNodes
     .filter(n => _.includes(newOrUpdatedEntries, n.id))
     .forEach(n => {

packages/gatsby-source-shopify/src/lib.js

@@ -47,9 +47,9 @@ export const queryAll = async (
   const edges = get([...path, `edges`], data)
   const nodes = edges.map(edge => edge.node)
 
-  aggregatedResponse
-    ? (aggregatedResponse = aggregatedResponse.concat(nodes))
-    : (aggregatedResponse = nodes)
+  aggregatedResponse = aggregatedResponse
+    ? aggregatedResponse.concat(nodes)
+    : nodes
 
   if (get([...path, `pageInfo`, `hasNextPage`], false, data))
     return queryAll(

packages/gatsby/src/utils/websocket-manager.js

@@ -103,8 +103,8 @@ class WebsocketManager {
     this.pageResults = new Map()
     this.staticQueryResults = new Map()
     this.errors = new Map()
-    this.websocket
-    this.programDir
+    // this.websocket
+    // this.programDir
 
     this.init = this.init.bind(this)
     this.getSocket = this.getSocket.bind(this)

starters/blog/.eslintrc.js

@@ -12,7 +12,7 @@ module.exports = {
   "parserOptions": {
     "sourceType": "module",
     "ecmaFeatures": {
-      "experimentalObjectRestSpread": true,
+      "ecmaVersion": 2018,
       "jsx": true,
     },
   }