2 files changed, 40 insertions, 3 deletions

diff --git a/std/wasi/snapshot_preview1.ts b/std/wasi/snapshot_preview1.ts
index 4c974fe1d..30756fe82 100644
--- a/std/wasi/snapshot_preview1.ts
+++ b/std/wasi/snapshot_preview1.ts
@@ -207,6 +207,10 @@ function syscall<T extends CallableFunction>(target: T) {
     try {
       return target(...args);
     } catch (err) {
+      if (err instanceof ExitStatus) {
+        throw err;
+      }
+
       switch (err.name) {
         case "NotFound":
           return ERRNO_NOENT;
@@ -266,15 +270,25 @@ interface FileDescriptor {
   entries?: Deno.DirEntry[];
 }
 
+export class ExitStatus {
+  code: number;
+
+  constructor(code: number) {
+    this.code = code;
+  }
+}
+
 export interface ContextOptions {
   args?: string[];
   env?: { [key: string]: string | undefined };
   preopens?: { [key: string]: string };
+  exitOnReturn?: boolean;
 }
 
 export default class Context {
   args: string[];
   env: { [key: string]: string | undefined };
+  exitOnReturn: boolean;
   memory: WebAssembly.Memory;
 
   fds: FileDescriptor[];
@@ -284,6 +298,7 @@ export default class Context {
   constructor(options: ContextOptions) {
     this.args = options.args ? options.args : [];
     this.env = options.env ? options.env : {};
+    this.exitOnReturn = options.exitOnReturn ?? true;
     this.memory = null!;
 
     this.fds = [
@@ -1497,7 +1512,11 @@ export default class Context {
       "proc_exit": syscall((
         rval: number,
       ): never => {
-        Deno.exit(rval);
+        if (this.exitOnReturn) {
+          Deno.exit(rval);
+        }
+
+        throw new ExitStatus(rval);
       }),
 
       "proc_raise": syscall((
diff --git a/std/wasi/snapshot_preview1_test.ts b/std/wasi/snapshot_preview1_test.ts
index d7e29e195..01b91bc3e 100644
--- a/std/wasi/snapshot_preview1_test.ts
+++ b/std/wasi/snapshot_preview1_test.ts
@@ -1,6 +1,6 @@
 // Copyright 2018-2020 the Deno authors. All rights reserved. MIT license.
-import Context from "./snapshot_preview1.ts";
-import { assertEquals, assertThrows } from "../testing/asserts.ts";
+import Context, { ExitStatus } from "./snapshot_preview1.ts";
+import { assert, assertEquals, assertThrows } from "../testing/asserts.ts";
 import { copy } from "../fs/mod.ts";
 import * as path from "../path/mod.ts";
 
@@ -179,6 +179,24 @@ Deno.test("context_start", function () {
     TypeError,
     "export _start must be a function",
   );
+
+  try {
+    const context = new Context({
+      exitOnReturn: false,
+    });
+    context.start({
+      exports: {
+        _start() {
+          const exit = context.exports["proc_exit"] as CallableFunction;
+          exit(0);
+        },
+        memory: new WebAssembly.Memory({ initial: 1 }),
+      },
+    });
+  } catch (err) {
+    assert(err instanceof ExitStatus);
+    assertEquals(err.code, 0);
+  }
 });
 
 Deno.test("context_initialize", function () {