8 files changed, 37 insertions, 0 deletions
diff --git a/cli/js/lib.deno.unstable.d.ts b/cli/js/lib.deno.unstable.d.ts
index aebd7f964..dc50416fc 100644
--- a/cli/js/lib.deno.unstable.d.ts
+++ b/cli/js/lib.deno.unstable.d.ts
@@ -1245,4 +1245,7 @@ declare namespace Deno {
    *  Requires `allow-env` permission.
    */
   export function hostname(): string;
+
+  /** **UNSTABLE**: The URL of the file that was originally executed from the command-line. */
+  export const mainModule: string;
 }
diff --git a/cli/js/ops/runtime.ts b/cli/js/ops/runtime.ts
index 632424327..70addf469 100644
--- a/cli/js/ops/runtime.ts
+++ b/cli/js/ops/runtime.ts
@@ -21,6 +21,10 @@ export function opStart(): Start {
   return sendSync("op_start");
 }
 
+export function opMainModule(): string {
+  return sendSync("op_main_module");
+}
+
 export interface Metrics {
   opsDispatched: number;
   opsDispatchedSync: number;
diff --git a/cli/js/runtime_main.ts b/cli/js/runtime_main.ts
index 58405f673..25a6b0f93 100644
--- a/cli/js/runtime_main.ts
+++ b/cli/js/runtime_main.ts
@@ -9,6 +9,7 @@
 
 import * as denoNs from "./deno.ts";
 import * as denoUnstableNs from "./deno_unstable.ts";
+import { opMainModule } from "./ops/runtime.ts";
 import { exit } from "./ops/os.ts";
 import {
   readOnly,
@@ -106,6 +107,7 @@ export function bootstrapMainRuntime(): void {
   if (unstableFlag) {
     Object.defineProperties(globalThis, unstableMethods);
     Object.defineProperties(globalThis, unstableProperties);
+    Object.defineProperty(denoNs, "mainModule", getterOnly(opMainModule));
     Object.assign(denoNs, denoUnstableNs);
   }
 
diff --git a/cli/ops/runtime.rs b/cli/ops/runtime.rs
index a85ce4011..e47b40792 100644
--- a/cli/ops/runtime.rs
+++ b/cli/ops/runtime.rs
@@ -6,11 +6,13 @@ use crate::state::State;
 use crate::version;
 use crate::DenoSubcommand;
 use deno_core::CoreIsolate;
+use deno_core::ModuleSpecifier;
 use deno_core::ZeroCopyBuf;
 use std::env;
 
 pub fn init(i: &mut CoreIsolate, s: &State) {
   i.register_op("op_start", s.stateful_json_op(op_start));
+  i.register_op("op_main_module", s.stateful_json_op(op_main_module));
   i.register_op("op_metrics", s.stateful_json_op(op_metrics));
 }
 
@@ -39,6 +41,21 @@ fn op_start(
   })))
 }
 
+fn op_main_module(
+  state: &State,
+  _args: Value,
+  _zero_copy: &mut [ZeroCopyBuf],
+) -> Result<JsonOp, OpError> {
+  let main = &state.borrow().main_module.to_string();
+  let main_url = ModuleSpecifier::resolve_url_or_path(&main)?;
+  if main_url.as_url().scheme() == "file" {
+    let main_path = std::env::current_dir().unwrap().join(main_url.to_string());
+    state.check_read_blind(&main_path, "main_module")?;
+  }
+  state.check_unstable("Deno.mainModule");
+  Ok(JsonOp::Sync(json!(&main)))
+}
+
 fn op_metrics(
   state: &State,
   _args: Value,
diff --git a/cli/tests/integration_tests.rs b/cli/tests/integration_tests.rs
index e3f4bd085..9c59e2a74 100644
--- a/cli/tests/integration_tests.rs
+++ b/cli/tests/integration_tests.rs
@@ -1708,6 +1708,11 @@ itest!(import_meta {
   output: "import_meta.ts.out",
 });
 
+itest!(main_module {
+  args: "run --quiet --unstable --allow-read --reload main_module.ts",
+  output: "main_module.ts.out",
+});
+
 itest!(lib_ref {
   args: "run --quiet --unstable --reload lib_ref.ts",
   output: "lib_ref.ts.out",
diff --git a/cli/tests/main_module.ts b/cli/tests/main_module.ts
new file mode 100644
index 000000000..19988f4bf
--- /dev/null
+++ b/cli/tests/main_module.ts
@@ -0,0 +1,3 @@
+console.log("main_module", Deno.mainModule);
+
+import "./main_module2.ts";
diff --git a/cli/tests/main_module.ts.out b/cli/tests/main_module.ts.out
new file mode 100644
index 000000000..31adb20cb
--- /dev/null
+++ b/cli/tests/main_module.ts.out
@@ -0,0 +1,2 @@
+main_module2 [WILDCARD]tests/main_module.ts
+main_module [WILDCARD]tests/main_module.ts
diff --git a/cli/tests/main_module2.ts b/cli/tests/main_module2.ts
new file mode 100644
index 000000000..585615c7f
--- /dev/null
+++ b/cli/tests/main_module2.ts
@@ -0,0 +1 @@
+console.log("main_module2", Deno.mainModule);