1 files changed, 62 insertions, 0 deletions
diff --git a/extensions/web/05_base64.js b/extensions/web/05_base64.js
new file mode 100644
index 000000000..4c51d88f1
--- /dev/null
+++ b/extensions/web/05_base64.js
@@ -0,0 +1,62 @@
+// Copyright 2018-2021 the Deno authors. All rights reserved. MIT license.
+
+// @ts-check
+/// <reference path="../webidl/internal.d.ts" />
+/// <reference path="../web/internal.d.ts" />
+/// <reference lib="esnext" />
+
+"use strict";
+
+((window) => {
+  const webidl = window.__bootstrap.webidl;
+  const {
+    forgivingBase64Encode,
+    forgivingBase64Decode,
+  } = window.__bootstrap.infra;
+
+  /**
+   * @param {string} data
+   * @returns {string}
+   */
+  function atob(data) {
+    data = webidl.converters.DOMString(data, {
+      prefix: "Failed to execute 'atob'",
+      context: "Argument 1",
+    });
+
+    const uint8Array = forgivingBase64Decode(data);
+    const result = [...uint8Array]
+      .map((byte) => String.fromCharCode(byte))
+      .join("");
+    return result;
+  }
+
+  /**
+   * @param {string} data
+   * @returns {string}
+   */
+  function btoa(data) {
+    const prefix = "Failed to execute 'btoa'";
+    webidl.requiredArguments(arguments.length, 1, { prefix });
+    data = webidl.converters.DOMString(data, {
+      prefix,
+      context: "Argument 1",
+    });
+    const byteArray = [...data].map((char) => {
+      const charCode = char.charCodeAt(0);
+      if (charCode > 0xff) {
+        throw new DOMException(
+          "The string to be encoded contains characters outside of the Latin1 range.",
+          "InvalidCharacterError",
+        );
+      }
+      return charCode;
+    });
+    return forgivingBase64Encode(Uint8Array.from(byteArray));
+  }
+
+  window.__bootstrap.base64 = {
+    atob,
+    btoa,
+  };
+})(globalThis);