--- a/.eslintignore
+++ b/.eslintignore
@@ -104,16 +104,17 @@ devtools/client/sourceeditor/**
 devtools/client/webaudioeditor/**
 devtools/client/webconsole/**
 !devtools/client/webconsole/panel.js
 !devtools/client/webconsole/jsterm.js
 !devtools/client/webconsole/console-commands.js
 devtools/client/webide/**
 !devtools/client/webide/components/webideCli.js
 devtools/server/**
+!devtools/server/child.js
 !devtools/server/actors/webbrowser.js
 !devtools/server/actors/styles.js
 !devtools/server/actors/string.js
 devtools/shared/*.js
 !devtools/shared/css-lexer.js
 !devtools/shared/defer.js
 !devtools/shared/event-emitter.js
 !devtools/shared/task.js

--- a/devtools/server/child.js
+++ b/devtools/server/child.js
@@ -1,38 +1,37 @@
 /* This Source Code Form is subject to the terms of the Mozilla Public
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 "use strict";
 
+/* global addMessageListener, removeMessageListener, sendAsyncMessage */
+
 try {
-
   var chromeGlobal = this;
 
-// Encapsulate in its own scope to allows loading this frame script
-// more than once.
+  // Encapsulate in its own scope to allows loading this frame script more than once.
   (function () {
     let Cu = Components.utils;
     let { require } = Cu.import("resource://devtools/shared/Loader.jsm", {});
     const DevToolsUtils = require("devtools/shared/DevToolsUtils");
     const { dumpn } = DevToolsUtils;
     const { DebuggerServer, ActorPool } = require("devtools/server/main");
 
-  // Note that this frame script may be evaluated in non-e10s build
-  // In such case, DebuggerServer is already going to be initialized.
+    // Note that this frame script may be evaluated in non-e10s build. In such case,
+    // DebuggerServer is already going to be initialized.
     if (!DebuggerServer.initialized) {
       DebuggerServer.init();
       DebuggerServer.isInChildProcess = true;
     }
 
-  // In case of apps being loaded in parent process, DebuggerServer is already
-  // initialized, but child specific actors are not registered.
-  // Otherwise, for apps in child process, we need to load actors the first
-  // time we load child.js
+    // In case of apps being loaded in parent process, DebuggerServer is already
+    // initialized, but child specific actors are not registered. Otherwise, for apps in
+    // child process, we need to load actors the first time we load child.js.
     DebuggerServer.addChildActors();
 
     let connections = new Map();
 
     let onConnect = DevToolsUtils.makeInfallible(function (msg) {
       removeMessageListener("debug:connect", onConnect);
 
       let mm = msg.target;
@@ -47,72 +46,67 @@ try {
       actorPool.addActor(actor);
       conn.addActorPool(actorPool);
 
       sendAsyncMessage("debug:actor", {actor: actor.form(), prefix: prefix});
     });
 
     addMessageListener("debug:connect", onConnect);
 
-  // Allows executing module setup helper from the parent process.
-  // See also: DebuggerServer.setupInChild()
+    // Allows executing module setup helper from the parent process.
+    // See also: DebuggerServer.setupInChild()
     let onSetupInChild = DevToolsUtils.makeInfallible(msg => {
       let { module, setupChild, args } = msg.data;
-      let m, fn;
+      let m;
 
       try {
         m = require(module);
 
         if (!setupChild in m) {
-          dumpn("ERROR: module '" + module + "' does not export '" +
-              setupChild + "'");
+          dumpn(`ERROR: module '${module}' does not export 'setupChild'`);
           return false;
         }
 
         m[setupChild].apply(m, args);
-
       } catch (e) {
-        let error_msg = "exception during actor module setup running in the child process: ";
-        DevToolsUtils.reportException(error_msg + e);
-        dumpn("ERROR: " + error_msg + " \n\t module: '" + module +
-            "' \n\t setupChild: '" + setupChild + "'\n" +
-            DevToolsUtils.safeErrorString(e));
+        let errorMessage =
+          "Exception during actor module setup running in the child process: ";
+        DevToolsUtils.reportException(errorMessage + e);
+        dumpn(`ERROR: ${errorMessage}\n\t module: '${module}'\n\t ` +
+              `setupChild: '${setupChild}'\n${DevToolsUtils.safeErrorString(e)}`);
         return false;
       }
       if (msg.data.id) {
-      // Send a message back to know when it is processed
-        sendAsyncMessage("debug:setup-in-child-response",
-                       {id: msg.data.id});
+        // Send a message back to know when it is processed
+        sendAsyncMessage("debug:setup-in-child-response", {id: msg.data.id});
       }
       return true;
     });
 
     addMessageListener("debug:setup-in-child", onSetupInChild);
 
     let onDisconnect = DevToolsUtils.makeInfallible(function (msg) {
       removeMessageListener("debug:disconnect", onDisconnect);
 
-    // Call DebuggerServerConnection.close to destroy all child actors
-    // (It should end up calling DebuggerServerConnection.onClosed
-    // that would actually cleanup all actor pools)
+      // Call DebuggerServerConnection.close to destroy all child actors. It should end up
+      // calling DebuggerServerConnection.onClosed that would actually cleanup all actor
+      // pools.
       let prefix = msg.data.prefix;
       let conn = connections.get(prefix);
       if (conn) {
         conn.close();
         connections.delete(prefix);
       }
     });
     addMessageListener("debug:disconnect", onDisconnect);
 
     let onInspect = DevToolsUtils.makeInfallible(function (msg) {
-    // Store the node to be inspected in a global variable
-    // (gInspectingNode). Later we'll fetch this variable again using
-    // the findInspectingNode request over the remote debugging
-    // protocol.
+      // Store the node to be inspected in a global variable (gInspectingNode). Later
+      // we'll fetch this variable again using the findInspectingNode request over the
+      // remote debugging protocol.
       let inspector = require("devtools/server/actors/inspector");
       inspector.setInspectingNode(msg.objects.node);
     });
     addMessageListener("debug:inspect", onInspect);
   })();
-
 } catch (e) {
-  dump("Exception in app child process: " + e + "\n");
+  dump(`Exception in app child process: ${e}\n`);
 }