JavaScript to Base64

Encode any JavaScript string to Base64 for use in HTTP headers, data URIs, API payloads, and localStorage values. Includes the equivalent btoa() browser snippet and Node.js Buffer.from() code.

Last updated: May 28, 2026

JavaScript string input

URL-safe(uses - _ instead of + /)

Base64 output

JS tip: Plain btoa() breaks on non-ASCII characters. Use the UTF-8-safe snippet shown after encoding, or Buffer.from(str, "utf8").toString("base64") in Node.js.

Client-Side Processing

Input Data Stays on Device

Instant Local Execution

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What is JavaScript to Base64?

JavaScript developers encode strings to Base64 when building Basic Auth headers, constructing data URIs for inline assets, preparing JWT-style payloads, or embedding binary content in JSON. The browser API is btoa(), Node.js uses Buffer.from(str).toString("base64"), and modern code often needs URL-safe output for JWT and URL parameters.

This tool encodes any string to Base64 with correct UTF-8 handling (plain btoa() breaks on non-ASCII characters) and shows the equivalent code so you can reproduce the encoding in your project.

How to Use JavaScript to Base64

Type or paste the JavaScript string you want to encode

Click "Encode to Base64" to generate the encoded output

Enable URL-safe mode if the result will appear in a URL or JWT

Copy the output or use the shown JS snippet in your code

Common Use Cases

Frontend developers encoding credentials for HTTP Basic Auth headers in fetch() or XMLHttpRequest calls.
React/Vue developers creating data URIs for inline SVGs or small image assets.
Node.js engineers encoding Buffer content to Base64 for JSON-safe transmission.
JavaScript developers encoding JSON config objects to pass as URL parameters or localStorage values.
JWT implementers encoding header and payload objects before signing.

Example Input and Output

Encoding a JavaScript config object to Base64 for embedding in a URL parameter.

JavaScript string

{"env":"production","debug":false}

Base64 output

eyJlbnYiOiJwcm9kdWN0aW9uIiwiZGVidWciOmZhbHNlfQ==

Node.js snippet

Buffer.from(str, "utf8").toString("base64") is the idiomatic Node.js approach and handles UTF-8 correctly without the TextEncoder workaround needed for browser btoa().

Browser-side only

Encoding runs locally in your browser. Nothing is transmitted.

Frequently Asked Questions

Why does btoa() fail on non-ASCII strings?

btoa() only handles Latin-1 characters. For UTF-8 strings (emojis, accented chars, CJK), you must encode to UTF-8 bytes first. This tool handles that automatically.

What is the correct way to Base64-encode UTF-8 in JavaScript?

Use TextEncoder to get UTF-8 bytes, then encode with btoa: btoa(String.fromCharCode(...new TextEncoder().encode(str))). In Node.js: Buffer.from(str, "utf8").toString("base64").

When should I use URL-safe Base64?

Use URL-safe mode when the encoded string will appear in a URL query parameter, a JWT, a cookie, or a filename. It replaces + with - and / with _ and removes = padding.

Is my data sent to a server?

No. Encoding runs entirely in your browser.