btoa() global function
The btoa()
method creates a
Base64-encoded ASCII string from a binary string (i.e., a
string in which each character in the string is treated as a byte
of binary data).
You can use this method to encode data which may otherwise cause communication
problems, transmit it, then use the atob()
method to decode the data again. For example, you can encode control
characters such as ASCII values 0 through 31.
Syntax
js
btoa(stringToEncode)
Parameters
stringToEncode
-
The binary string to encode.
Return value
An ASCII string containing the Base64 representation of
stringToEncode
.
Exceptions
InvalidCharacterError
DOMException
-
The string contained a character that did not fit in a single byte. See "Unicode strings" below for more detail.
Examples
js
const encodedData = btoa("Hello, world"); // encode a string
const decodedData = atob(encodedData); // decode the string
Unicode strings
Base64, by design, expects binary data as its input. In terms of JavaScript strings,
this means strings in which the code point of each character occupies only one byte. So if you pass a
string into btoa()
containing characters that occupy more than one byte,
you will get an error, because this is not considered binary data:
js
const ok = "a";
console.log(ok.codePointAt(0).toString(16)); // 61: occupies < 1 byte
const notOK = "✓";
console.log(notOK.codePointAt(0).toString(16)); // 2713: occupies > 1 byte
console.log(btoa(ok)); // YQ==
console.log(btoa(notOK)); // error
For how to work around this limitation when dealing with arbitrary Unicode text, see The "Unicode Problem" section of the Base64 glossary entry.
Specifications
Specification |
---|
HTML Standard # dom-btoa-dev |
Browser compatibility
BCD tables only load in the browser
See also
- A polyfill of
btoa
is available incore-js
data
URLsatob()
- Base64