JS DOM: encodeURI, decodeURI

Method encodeURI

encodeURI is a string property of the the Global Object.

encodeURI(str)

Return a new string such that illegal URL characters in str are percent encoded.

This encoding is called percent encoding. It is required for all non-ASCII chars in the URI. (but usually browsers can handle it fine without percent encoding.)

• Each encoded character is changed to the form %ab, repeated 1 to 4 times
• Where a or b is a hexadecimal digit.
• The 2 digits hexadecimal represents a byte (8 bits).
• The sequence of bytes together is the character in Unicode: UTF-8 Encoding

// encode a URL that contains space

console.log(
 encodeURI ( "http://example.com/a b.jpg" ) ===
 "http://example.com/a%20b.jpg"
);

// true

Example: Encode Chinese Characters

// encode Chinese characters

console.log(
encodeURI("中文") === "%E4%B8%AD%E6%96%87"
);
// true

/*
中
codepoint 20013
hexadecimal 4e2d
utf8 encoding: E4 B8 AD

文
codepoint 25991
hexadecimal 6587
utf8 encoding: E6 96 87
*/

Example: Encode a emoji

// encode a emoji
console.log( encodeURI("🦋"));
// %F0%9F%A6%8B

/*
🦋
Name: BUTTERFLY
ID 129419
HEXD 1F98B
UTF8  F0 9F A6 8B
UTF16 D83E DD8B
*/

What characters are changed by encodeURI?

{ } [ ] < > % | \ ^ " `

And all non-ASCII Unicode are also changed.

// all chars that encodeURI() does not change

console.log((Array.from((Array(128)).keys(), (x) => String.fromCharCode(x)).filter((x) => (encodeURI(x) === x))).join(""));
// !#$&'()*+,-./0123456789:;=?@ABCDEFGHIJKLMNOPQRSTUVWXYZ_abcdefghijklmnopqrstuvwxyz~