diff --git a/README.md b/README.md
index b65e141fa5..2694437da4 100644
--- a/README.md
+++ b/README.md
@@ -2,12 +2,12 @@
 
 [![Build Status](https://travis-ci.com/ry/deno.svg?branch=master)](https://travis-ci.com/ry/deno)
 
-A secure TypeScript runtime on V8
+## A secure TypeScript runtime built on V8
 
 * Supports TypeScript 2.8 out of the box. Uses V8 6.8.275.3. That is, it's
   very modern JavaScript.
 
-* No package.json, no npm. Not explicitly compatible with Node.
+* No `package.json`. No npm. Not explicitly compatible with Node.
 
 * Imports reference source code URLs only.
 	```
@@ -15,14 +15,14 @@ A secure TypeScript runtime on V8
   import { log } from "./util.ts"
 	```
   Remote code is fetched and cached on first execution, and never updated until
-  the code is run with the `--reload` flag. (So this will still work on an
+  the code is run with the `--reload` flag. (So, this will still work on an
   airplane. See `~/.deno/src` for details on the cache.)
 
 * File system and network access can be controlled in order to run sandboxed
   code. Defaults to read-only file system access and no network access.
 	Access between V8 (unprivileged) and Golang (privileged) is only done via
   serialized messages defined in this
-  [protobuf](https://github.com/ry/deno/blob/master/msg.proto), this makes it
+  [protobuf](https://github.com/ry/deno/blob/master/msg.proto). This makes it
   easy to audit.
 	To enable write access explicitly use `--allow-write` and `--allow-net` for
   network access.
@@ -43,7 +43,7 @@ A secure TypeScript runtime on V8
 
 * Always dies on uncaught errors.
 
-* Supports top-level await.
+* Supports top-level `await`.
 
 * Aims to be browser compatible.
 
@@ -61,17 +61,18 @@ And examples are around here: [testdata/004_set_timeout.ts](https://github.com/r
 
 Roadmap is [here](https://github.com/ry/deno/blob/master/TODO.txt).
 
-Also see this preentation http://tinyclouds.org/jsconf2018.pdf
+Also see this presentation: http://tinyclouds.org/jsconf2018.pdf
 
 
 ## Compile instructions
 
-I will release binaries at some point but for now you have to build it
+I will release binaries at some point, but for now you have to build it
 yourself.
 
-You will need [Go](https://golang.org/) with `$GOPATH` defined and
-`$GOPATH/bin` in your `$PATH`.  You will also need
-[yarn](https://yarnpkg.com/lang/en/docs/install/) installed.
+You will need [Go](https://golang.org) with `$GOPATH` defined and
+`$GOPATH/bin` in your `$PATH`.  
+
+You will also need [yarn](https://yarnpkg.com/lang/en/docs/install/) installed.
 
 You need Protobuf 3. On Linux this might work:
 
@@ -111,9 +112,9 @@ go get -u github.com/ry/v8worker2
 cd $GOPATH/src/github.com/ry/v8worker2
 ./build.py --use_ccache
 ```
-Maybe also run `git submodule update --init` in the v8worker2 dir.
+Maybe also run `git submodule update --init` in the `v8worker2/` dir.
 
-Finally you can get `deno` and its other Go deps.
+Finally, you can get `deno` and its other Go deps.
 
 ``` bash
 go get -u github.com/ry/deno/...
@@ -129,7 +130,7 @@ make # Wait for redacted
 ./deno testdata/001_hello.js # Output: Hello World
 ```
 
-## make commands
+## `make` commands
 
 ``` bash
 make deno # Builds the deno executable.
diff --git a/deno_dir.go b/deno_dir.go
index 166fcb8270..2df1f74b4b 100644
--- a/deno_dir.go
+++ b/deno_dir.go
@@ -56,7 +56,7 @@ func FetchRemoteSource(remoteUrl string, localFilename string) ([]byte, error) {
 			return nil, err
 		}
 
-		// Write to to file. Need to reopen it for writing.
+		// Write to local file. Need to reopen it for writing.
 		file, err = os.OpenFile(localFilename, os.O_RDWR|os.O_CREATE, 0700)
 		if err != nil {
 			return nil, err
diff --git a/main.go b/main.go
index 465c8b5ea3..37cfd022d4 100644
--- a/main.go
+++ b/main.go
@@ -5,15 +5,17 @@ package deno
 import (
 	"flag"
 	"fmt"
-	"github.com/ry/v8worker2"
 	"os"
 	"runtime/pprof"
+
+	"github.com/ry/v8worker2"
 )
 
 var flagReload = flag.Bool("reload", false, "Reload cached remote source code.")
 var flagV8Options = flag.Bool("v8-options", false, "Print V8 command line options.")
 var flagDebug = flag.Bool("debug", false, "Enable debug output.")
-var flagGoProf = flag.String("goprof", "", "Write golang cpu profile to file.")
+var flagCPUProf = flag.String("cpuprof", "", "Write golang cpu profile to file.")
+var flagMemProf = flag.String("memprof", "", "Write golang memory profile to file.")
 
 var flagAllowRead = flag.Bool("allow-read", true,
 	"Allow program to read file system.")
@@ -22,6 +24,8 @@ var flagAllowWrite = flag.Bool("allow-write", false,
 var flagAllowNet = flag.Bool("allow-net", false,
 	"Allow program to make network connection.")
 
+var memProfile *os.File
+
 var Perms struct {
 	FsRead  bool
 	FsWrite bool
@@ -72,14 +76,9 @@ func Init() {
 		os.Exit(1)
 	}
 
-	// Maybe start Golang CPU profiler.
+	// Maybe start Golang profilers.
 	// Use --prof for profiling JS.
-	if *flagGoProf != "" {
-		f, err := os.Create(*flagGoProf)
-		check(err)
-		pprof.StartCPUProfile(f)
-		defer pprof.StopCPUProfile()
-	}
+	StartProfiling()
 
 	createDirs()
 	InitOS()
@@ -95,6 +94,29 @@ func Init() {
 	main_map = stringAsset("main.map")
 }
 
+func StartProfiling() {
+	if *flagCPUProf != "" {
+		cpuProfile, err := os.Create(*flagCPUProf)
+		check(err)
+		check(pprof.StartCPUProfile(cpuProfile))
+	}
+	if *flagMemProf != "" {
+		var err error
+		memProfile, err = os.Create(*flagMemProf)
+		check(err)
+		check(pprof.WriteHeapProfile(memProfile))
+	}
+}
+
+func stopProfiling() {
+	if *flagCPUProf != "" {
+		pprof.StopCPUProfile()
+	}
+	if *flagMemProf != "" {
+		check(memProfile.Close())
+	}
+}
+
 // It's up to library users to call
 // deno.Eval("deno_main.js", "denoMain()")
 func Eval(filename string, code string) {
@@ -114,4 +136,5 @@ func Loop() {
 		StartMainMap:   main_map,
 	})
 	DispatchLoop()
+	stopProfiling()
 }
diff --git a/runtime.ts b/runtime.ts
index 6bc09dd89e..8929b7112c 100644
--- a/runtime.ts
+++ b/runtime.ts
@@ -59,7 +59,7 @@ export function setup(mainJs: string, mainMap: string): void {
 // FileModule.load(). FileModules are NOT executed upon first load, only when
 // compileAndRun is called.
 export class FileModule {
-  scriptVersion: string = undefined;
+  scriptVersion: string;
   readonly exports = {};
 
   private static readonly map = new Map<string, FileModule>();
@@ -80,7 +80,7 @@ export class FileModule {
 
   compileAndRun(): void {
     if (!this.outputCode) {
-      // If there is no cached outputCode, the compile the code.
+      // If there is no cached outputCode, then compile the code.
       util.assert(
         this.sourceCode != null && this.sourceCode.length > 0,
         `Have no source code from ${this.fileName}`
diff --git a/timers.ts b/timers.ts
index cddb859d9a..ed65128cda 100644
--- a/timers.ts
+++ b/timers.ts
@@ -81,6 +81,7 @@ export function setInterval(
 }
 
 export function clearTimer(id: number) {
+  timers.delete(id);
   pubInternal("timers", {
     command: pb.Msg.Command.TIMER_CLEAR,
     timerClearId: id