1 files changed, 80 insertions, 0 deletions
diff --git a/runtime/js/41_prompt.js b/runtime/js/41_prompt.js
new file mode 100644
index 000000000..ec294668b
--- /dev/null
+++ b/runtime/js/41_prompt.js
@@ -0,0 +1,80 @@
+// Copyright 2018-2020 the Deno authors. All rights reserved. MIT license.
+((window) => {
+  const { stdin } = window.__bootstrap.files;
+  const { isatty } = window.__bootstrap.tty;
+  const LF = "\n".charCodeAt(0);
+  const CR = "\r".charCodeAt(0);
+  const decoder = new TextDecoder();
+  const core = window.Deno.core;
+
+  function alert(message = "Alert") {
+    if (!isatty(stdin.rid)) {
+      return;
+    }
+
+    core.print(`${message} [Enter] `, false);
+
+    readLineFromStdinSync();
+  }
+
+  function confirm(message = "Confirm") {
+    if (!isatty(stdin.rid)) {
+      return false;
+    }
+
+    core.print(`${message} [y/N] `, false);
+
+    const answer = readLineFromStdinSync();
+
+    return answer === "Y" || answer === "y";
+  }
+
+  function prompt(message = "Prompt", defaultValue) {
+    defaultValue ??= null;
+
+    if (!isatty(stdin.rid)) {
+      return null;
+    }
+
+    core.print(`${message} `, false);
+
+    if (defaultValue) {
+      core.print(`[${defaultValue}] `, false);
+    }
+
+    return readLineFromStdinSync() || defaultValue;
+  }
+
+  function readLineFromStdinSync() {
+    const c = new Uint8Array(1);
+    const buf = [];
+
+    while (true) {
+      const n = stdin.readSync(c);
+      if (n === null || n === 0) {
+        break;
+      }
+      if (c[0] === CR) {
+        const n = stdin.readSync(c);
+        if (c[0] === LF) {
+          break;
+        }
+        buf.push(CR);
+        if (n === null || n === 0) {
+          break;
+        }
+      }
+      if (c[0] === LF) {
+        break;
+      }
+      buf.push(c[0]);
+    }
+    return decoder.decode(new Uint8Array(buf));
+  }
+
+  window.__bootstrap.prompt = {
+    alert,
+    confirm,
+    prompt,
+  };
+})(this);