2 files changed, 70 insertions, 0 deletions
diff --git a/cli/rt/41_prompt.js b/cli/rt/41_prompt.js
new file mode 100644
index 000000000..5a588def1
--- /dev/null
+++ b/cli/rt/41_prompt.js
@@ -0,0 +1,66 @@
+// Copyright 2018-2020 the Deno authors. All rights reserved. MIT license.
+((window) => {
+  const { stdin, stdout } = window.__bootstrap.files;
+  const { isatty } = window.__bootstrap.tty;
+  const LF = "\n".charCodeAt(0);
+  const encoder = new TextEncoder();
+  const decoder = new TextDecoder();
+
+  function alert(message = "Alert") {
+    if (!isatty(stdin.rid)) {
+      return;
+    }
+
+    stdout.writeSync(encoder.encode(`${message} [Enter] `));
+
+    readLineFromStdinSync();
+  }
+
+  function confirm(message = "Confirm") {
+    if (!isatty(stdin.rid)) {
+      return false;
+    }
+
+    stdout.writeSync(encoder.encode(`${message} [y/N] `));
+
+    const answer = readLineFromStdinSync();
+
+    return answer === "Y" || answer === "y";
+  }
+
+  function prompt(message = "Prompt", defaultValue) {
+    defaultValue ??= null;
+
+    if (!isatty(stdin.rid)) {
+      return null;
+    }
+
+    stdout.writeSync(encoder.encode(`${message} `));
+
+    if (defaultValue) {
+      stdout.writeSync(encoder.encode(`[${defaultValue}] `));
+    }
+
+    return readLineFromStdinSync() || defaultValue;
+  }
+
+  function readLineFromStdinSync() {
+    const c = new Uint8Array(1);
+    const buf = [];
+
+    while (true) {
+      const n = stdin.readSync(c);
+      if (n === 0 || c[0] === LF) {
+        break;
+      }
+      buf.push(c[0]);
+    }
+    return decoder.decode(new Uint8Array(buf));
+  }
+
+  window.__bootstrap.prompt = {
+    alert,
+    confirm,
+    prompt,
+  };
+})(this);
diff --git a/cli/rt/99_main.js b/cli/rt/99_main.js
index d8c34bcb3..e33264726 100644
--- a/cli/rt/99_main.js
+++ b/cli/rt/99_main.js
@@ -27,6 +27,7 @@ delete Object.prototype.__proto__;
   const fileReader = window.__bootstrap.fileReader;
   const webSocket = window.__bootstrap.webSocket;
   const fetch = window.__bootstrap.fetch;
+  const prompt = window.__bootstrap.prompt;
   const denoNs = window.__bootstrap.denoNs;
   const denoNsUnstable = window.__bootstrap.denoNsUnstable;
   const errors = window.__bootstrap.errors.errors;
@@ -285,6 +286,9 @@ delete Object.prototype.__proto__;
     onunload: util.writable(null),
     close: util.writable(windowClose),
     closed: util.getterOnly(() => windowIsClosing),
+    alert: util.writable(prompt.alert),
+    confirm: util.writable(prompt.confirm),
+    prompt: util.writable(prompt.prompt),
   };
 
   const workerRuntimeGlobalProperties = {