JavaScript escape sequences
Escape sequences in a JavaScript string are used to express code units based on code point numbers and It is a mechanism for quoting a single character, Such as : quotes, backslash and control characters.
The backslash('\') is the escape character, JavaScript was built at a time when unicode was a 16-bit character set, so all character, make a string with just one character in it.
JavaScript has 3-escape types, one which was introduced in ECMAScript 2015 :
| # | Type | Range | Digits | Format | Example |
|---|---|---|---|---|---|
| 1 | Hexadecimal escape | 0x00 to 0xFF | 2 | \xDD | \x1E |
| 2 | Unicode escape | \251 | 4 | \uDDDD | \u006E |
| 3 | Codepoint escape | 0x00 to 0x10FFFF | 1 to 6 | \u{D..D} | \u{1F639} |
Let’s see them escape sequences in more detail :
1.) Unicode escape sequence :
The unicode escape sequence is \u<hex>, where \u is a prefix followed by a hexadecimal number <hex> with a fixed length of 4 digits.
If you want to escape code points from the entire BMP, then you can use an unicode escape sequence.
For example '\u000B1' (Plus OR Minus symbol '±') or '\u0222B' (Integral symbol '∫')
Let’s see the use of unicode escape sequences:
Example :
- <script>
const str = 'I\u0020learn \u0055nicode';
console.log(str); //=>'I learn Unicode'
const reg = /\u0055ni.*/;
console.log(reg.test('Unicode')); //=>true
- </script>
Important point of unicode escape sequence :
An unicode escape sequence can escape code points in a limited range: from U+0000 to U+FFFF (all BMP code points) because only 4 digits are allowed.
The unicode escape sequence most of the time this is enough to represent the commonly used symbols.
2.) Hexadecimal escape sequence :
The shortest form is named hexadecimal escape sequence: \x<hex>, where \x is a prefix followed by a hexadecimal number <hex> with a fixed length of 2 digits.
For example : '\x40' (symbol '@') or '\x3F' (symbol '?').
Let’s see the use of hexadecimal escape sequences :
Example :
The hexadecimal escape sequence in a string literal or regular expression looks this way.
- <script>
const str = 'I le\x61rn \x48\x65xadecimal';
console.log(str); //=>'I learn Hexadecimal'
const reg = /\x4A\x61va.*/;
console.log(reg.test('JavaScript')); //=>true
- </script>
Important point of hexadecimal escape sequence :
A hexadecimal escape sequence can escape code points in a limited range: from U+00 to U+FF because only 2 digits are allowed.
But hexadecimal escape is nice for use, Because it’s short.
3.) Codepoint escape sequence :
ECMAScript 2015 provides escape sequences that represent code points from the entire Unicode space: U+0000 to U+10FFFF, i.e. BMP and astral planes.
The new format is called code point escape sequence: \u{<hex>}, where <hex> is a hexadecimal number with a variable length of 1 to 6 digits.
For example : '\u{4B}' (symbol 'K') or '\u{1F620}' (Angry face symbol 😡).
Let’s see the use of Codepoint escape sequence :
Example :
- <script>
const str = 'Angry face \u{1F620}';
console.log(str); //=>'Angry face 😡'
const reg = /\u{1F620}/u;
console.log(reg.test('Angry face 😡')); //=>true
- </script>
Important point of Codepoint escape sequence :
Notice that the regular expression /\u{1F620}/u has a special flag u.
The following characters are reserved in JavaScript strings :
| # | Escape sequences | Result | Description |
|---|---|---|---|
| 1 | \' | ' | Single quotation |
| 2 | \" | " | Double quotation |
| 3 | \\ | \ | Backslash |
Seven other escape sequences are valid in JavaScript :
| # | Escape sequences | Description | Unicode |
|---|---|---|---|
| 1 | \b | Backspace | U+0008 |
| 2 | \f | Form feed | U+000C |
| 3 | \n | New line | U+000A |
| 4 | \r | Carriage Return | U+000D |
| 5 | \t | Horizontal Tabulator | U+0009 |
| 6 | \v | Vertical Tabulator | U+000B |
| 7 | \0 | null character | U+0000 |
Note : Important points of escape sequence;
'\0' : null character (U+0000 NULL) (only if the next character is not a decimal digit; else it is an octal escape sequence)
-
Escape sequences strings must be written within quotes,Otherwise JavaScript will misunderstand this string:
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