window.btoa() creates a Base64-encoded ASCII string from a binary string (MDN). Pair it with atob() to decode again.
Pass the required arguments shown below. Check return values and browser support before you rely on the result.
Call window.btoa. Start with this line.
btoa(stringToEncode)| Call | What it does |
|---|---|
btoa(stringToEncode) | Primary signature. |
window.btoa(...) | Call with the arguments your case needs. |
Built into the browser. Call window.btoa(...) (or the global btoa(...)) — no import required.
btoa(stringToEncode)| Parameter | Description |
|---|---|
| stringToEncode | Required. Binary string (code points < 256) |
| Return Value | Description |
|---|---|
| * | Base64 ASCII string |
Encode a short ASCII string to Base64.
const encoded = btoa("Hello, world");
console.log(encoded); // "SGVsbG8sIHdvcmxk"
// same as: window.btoa("Hello, world")btoa. Bytes are turned into Base64 text.SGVsbG8sIHdvcmxk.btoa and window.btoa match in browsers.atobEncode, then decode, to prove the pair is reversible for ASCII.
const original = "CodeToFun";
const encoded = btoa(original);
const decoded = atob(encoded);
console.log(encoded); // "Q29kZVRvRnVu"
console.log(decoded); // "CodeToFun"
console.log(decoded === original); // trueoriginal is ASCII-safe.btoa. You get Base64.atob. You get the same characters back.=== is true for this Latin-1 / ASCII case.MDN-style check: a Latin letter fits in one byte and encodes cleanly.
const ok = "a";
console.log(ok.codePointAt(0).toString(16)); // "61"
console.log(btoa(ok)); // "YQ==""a" is a single byte.61 is below FF.btoa("a") returns YQ==.255 are not allowed as raw input.Characters above one byte cause InvalidCharacterError.
const notOK = "✓";
console.log(notOK.codePointAt(0).toString(16)); // "2713"
try {
console.log(btoa(notOK));
} catch (err) {
console.log(err.name); // "InvalidCharacterError"
}✓ is not a single byte.2713 is greater than FF.btoa. The browser throws.InvalidCharacterError or convert to UTF-8 first.MDN-style path: TextEncoder → binary string → btoa.
function bytesToBase64(bytes) {
const binString = Array.from(bytes, (byte) =>
String.fromCodePoint(byte)
).join("");
return btoa(binString);
}
const text = "a ✓";
const encoded = bytesToBase64(new TextEncoder().encode(text));
console.log(encoded); // Base64 of UTF-8 bytesTextEncoder turns text into bytes.btoa. Now every character is a valid single byte.Uint8Array.prototype.toBase64().Window.btoa() is marked Baseline Widely available on MDN (since July 2015). Browser Window API — also available as a global in modern Node.js.
Encode binary strings to Base64 across modern browsers.
Bottom line: Safe for Base64 encoding of byte-safe / ASCII data. For Unicode text, convert to UTF-8 bytes first.
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