refactor: typescript support

helpers/utils/b64.ts

@@ -0,0 +1,32 @@
+export function decodeB64StringToArrayBuffer(input: string): ArrayBuffer {
+  const bytes = Math.floor((input.length / 4) * 3)
+  const ab = new ArrayBuffer(bytes)
+  const uarray = new Uint8Array(ab)
+
+  const keyStr =
+    "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/="
+
+  let chr1, chr2, chr3
+  let enc1, enc2, enc3, enc4
+  let j = 0
+
+  input = input.replace(/[^A-Za-z0-9+/=]/g, "")
+
+  for (let i = 0; i < bytes; i += 3) {
+    // get the 3 octets in 4 ASCII chars
+    enc1 = keyStr.indexOf(input.charAt(j++))
+    enc2 = keyStr.indexOf(input.charAt(j++))
+    enc3 = keyStr.indexOf(input.charAt(j++))
+    enc4 = keyStr.indexOf(input.charAt(j++))
+
+    chr1 = (enc1 << 2) | (enc2 >> 4)
+    chr2 = ((enc2 & 15) << 4) | (enc3 >> 2)
+    chr3 = ((enc3 & 3) << 6) | enc4
+
+    uarray[i] = chr1
+    if (enc3 !== 64) uarray[i + 1] = chr2
+    if (enc4 !== 64) uarray[i + 2] = chr3
+  }
+
+  return ab
+}