encodeURI()

The encodeURI() 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).

URI

A complete URI.

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

The encodeURI() function does not encode characters that have special meaning (reserved characters) for a URI. The following example shows all the parts that a URI "scheme" can possibly contain. Note how certain characters are used to signify special meaning:

http://username:password@www.example.com:80/path/to/file.php?foo=316&bar=this+has+spaces#anchor

Hence encodeURI() does not encode characters that are necessary to formulate a complete URI. Also, encodeURI() does not encode a few additional characters, known as "unreserved marks", which do not have a reserved purpose but are allowed in a URI "as is". (See RFC2396)

encodeURI() escapes all characters except:

Not Escaped:

    A-Z a-z 0-9 ; , / ? : @ & = + $ - _ . ! ~ * ' ( ) #

encodeURI() differs from encodeURIComponent() as follows:

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

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

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

Note that encodeURI() by itself cannot form proper HTTP GET and POST requests, such as for XMLHttpRequest, because "&", "+", and "=" are not encoded, which are treated as special characters in GET and POST requests. encodeURIComponent(), however, does encode these characters.

An 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(encodeURI('\uD800\uDFFF'));

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

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

If one wishes to follow the more recent RFC3986 for URLs, which makes square brackets reserved (for IPv6) and thus not encoded when forming something which could be part of a URL (such as a host), the following code snippet may help:

function fixedEncodeURI(str) {
    return encodeURI(str).replace(/%5B/g, '[').replace(/%5D/g, ']');
}

• decodeURI()
• encodeURIComponent()
• decodeURIComponent()