JS DOM: escape, unescape

By Xah Lee. Date: . Last updated: .

The Escape Method

escape is a string property of the the Global Object.

escape is deprecated.

escape(str)
Return a new string from str with some characters percent encoded.

some characters are replaced by this rule:

, where DD is 2 digits of hexadecimal and DDDD is 4 digits of hexadecimal. (note: a hexadecimal digit is 4 bits. So, 2 hexadecimal digits is 1 byte.)

The hexadecimal are the code unit of the character. (that is, the first 2 bytes of the character in UTF16)

〔see JS: String Code Unit〕

The chars that does not change are:

All other chars are replaced.

Example, not changed characters.

// not changed
console.log( escape ("a") === "a" );
// true

// not changed
console.log( escape (".") === "." );
// true

Example, changed characters.

// changed
console.log( escape (" ") === "%20" );
// true

// changed
console.log( escape (",") === "%2C" );
// true

NON-ASCII characters are all changed.

console.log( escape ( "α" ) === "%u03B1" );
// true

// α
// Name: GREEK SMALL LETTER ALPHA
// codepoint 945
// codepoint hexadecimal: 3b1

Example of Unicode character with codepoint ≥ 2^16.

console.log( escape ( "😂" ) === "%uD83D%uDE02" );
// true

// same as
console.log(
 "%u" +
 // first byte
 "😂". charCodeAt (0) .toString (16) . toUpperCase() +
 "%u" +
 // second byte
 "😂". charCodeAt (1) .toString (16) . toUpperCase()
);

// 😂
// name: FACE WITH TEARS OF JOY
// codepoint decimal: 128514
// codepoint hexadecimal: 1f602
// UTF 16 encoding: D8 3D DE 02

Check Which Character Are Changed

// print out all ASCII chars that escape() does not change

for (let i = 0; i < 128; i++) {
  let xchar = String.fromCharCode(i);
  if (escape(xchar) === xchar) {
    console.log(i + " " + xchar);
  }
}

/*

42 *
43 +
45 -
46 .
47 /
48 0
49 1
50 2
51 3
52 4
53 5
54 6
55 7
56 8
57 9
64 @
65 A
66 B
67 C
68 D
69 E
70 F
71 G
72 H
73 I
74 J
75 K
76 L
77 M
78 N
79 O
80 P
81 Q
82 R
83 S
84 T
85 U
86 V
87 W
88 X
89 Y
90 Z
95 _
97 a
98 b
99 c
100 d
101 e
102 f
103 g
104 h
105 i
106 j
107 k
108 l
109 m
110 n
111 o
112 p
113 q
114 r
115 s
116 t
117 u
118 v
119 w
120 x
121 y
122 z

 */

unescape

Use unescape function to decode a string encoded with escape.

JS encode decode URL