encodeURIComponent()

The encodeURIComponent() function encodes a URI by replacing each instance of certain characters by one, two, three, or four escape sequences representing the UTF-8 encoding of the character (will only be four escape sequences for characters composed of two "surrogate" characters).

The source for this interactive example is stored in a GitHub repository. If you'd like to contribute to the interactive examples project, please clone https://github.com/mdn/interactive-examples and send us a pull request.

Syntax

encodeURIComponent(str);

Parameters

str

String. A component of a URI.

Return value

A new string representing the provided string encoded as a URI component.

Description

encodeURIComponent() escapes all characters except:

Not Escaped:

    A-Z a-z 0-9 - _ . ! ~ * ' ( )

encodeURIComponent() differs from encodeURI as follows:

var set1 = ";,/?:@&=+$";  // Reserved Characters
var set2 = "-_.!~*'()";   // Unescaped Characters
var set3 = "#";           // Number Sign
var set4 = "ABC abc 123"; // Alphanumeric Characters + Space

console.log(encodeURI(set1)); // ;,/?:@&=+$
console.log(encodeURI(set2)); // -_.!~*'()
console.log(encodeURI(set3)); // #
console.log(encodeURI(set4)); // ABC%20abc%20123 (the space gets encoded as %20)

console.log(encodeURIComponent(set1)); // %3B%2C%2F%3F%3A%40%26%3D%2B%24
console.log(encodeURIComponent(set2)); // -_.!~*'()
console.log(encodeURIComponent(set3)); // %23
console.log(encodeURIComponent(set4)); // ABC%20abc%20123 (the space gets encoded as %20)

Note that a URIError will be thrown if one attempts to encode a surrogate which is not part of a high-low pair, e.g.,

// high-low pair ok
console.log(encodeURIComponent('\uD800\uDFFF'));

// lone high surrogate throws "URIError: malformed URI sequence"
console.log(encodeURIComponent('\uD800'));

// lone low surrogate throws "URIError: malformed URI sequence"
console.log(encodeURIComponent('\uDFFF'));

Use encodeURIComponent() on user-entered fields from forms POST'd to the server. This will encode "&" symbols that may inadvertently be generated during data entry for special HTML entities or other characters that require encoding/decoding.

For example, if a user writes "Jack & Jill", the text may get encoded as "Jack & Jill". Without encodeURIComponent() the ampersand could be interpretted on the server as the start of a new field and jeopardize the integrity of the data.

For application/x-www-form-urlencoded, spaces are to be replaced by "+", so one may wish to follow a encodeURIComponent() replacement with an additional replacement of "%20" with "+".

To be more stringent in adhering to RFC 3986 (which reserves !, ', (, ), and *), even though these characters have no formalized URI delimiting uses, the following can be safely used:

function fixedEncodeURIComponent(str) {
  return encodeURIComponent(str).replace(/[!'()*]/g, function(c) {
    return '%' + c.charCodeAt(0).toString(16);
  });
}

Examples

Encoding for Content-Disposition and Link headers

The following example provides the special encoding required within UTF-8 Content-Disposition and Link server response header parameters (e.g., UTF-8 filenames):

var fileName = 'my file(2).txt';
var header = "Content-Disposition: attachment; filename*=UTF-8''"
             + encodeRFC5987ValueChars(fileName);

console.log(header);
// logs "Content-Disposition: attachment; filename*=UTF-8''my%20file%282%29.txt"


function encodeRFC5987ValueChars(str) {
    return encodeURIComponent(str).
        // Note that although RFC3986 reserves "!", RFC5987 does not,
        // so we do not need to escape it
        replace(/['()]/g, escape). // i.e., %27 %28 %29
        replace(/\*/g, '%2A').
            // The following are not required for percent-encoding per RFC5987,
            // so we can allow for a little better readability over the wire: |`^
            replace(/%(?:7C|60|5E)/g, unescape);
}

// here is an alternative to the above function
function encodeRFC5987ValueChars2(str) {
  return encodeURIComponent(str).
    // Note that although RFC3986 reserves "!", RFC5987 does not,
    // so we do not need to escape it
    replace(/['()*]/g, c => "%" + c.charCodeAt(0).toString(16)). // i.e., %27 %28 %29 %2a (Note that valid encoding of "*" is %2A
                                                                 // which necessitates calling toUpperCase() to properly encode)
    // The following are not required for percent-encoding per RFC5987,
    // so we can allow for a little better readability over the wire: |`^
    replace(/%(7C|60|5E)/g, (str, hex) => String.fromCharCode(parseInt(hex, 16)));
}

Specifications

Browser compatibility

See also

• decodeURI
• encodeURI
• decodeURIComponent