Stage 3 Draft / November 27, 2024

RegExp.escape

22 Text Processing

22.2 RegExp (Regular Expression) Objects

22.2.5 Properties of the RegExp Constructor

22.2.5.1 RegExp.escape ( S )

This function returns a copy of S in which characters that are potentially special in a regular expression Pattern have been replaced by equivalent escape sequences.

It performs the following steps when called:

  1. If S is not a String, throw a TypeError exception.
  2. Let escaped be the empty String.
  3. Let cpList be StringToCodePoints(S).
  4. For each code point c of cpList, do
    1. If escaped is the empty String and c is matched by either DecimalDigit or AsciiLetter, then
      1. NOTE: Escaping a leading digit ensures that output corresponds with pattern text which may be used after a \0 character escape or a DecimalEscape such as \1 and still match S rather than be interpreted as an extension of the preceding escape sequence. Escaping a leading ASCII letter does the same for the context after \c.
      2. Let numericValue be the numeric value of c.
      3. Let hex be Number::toString(𝔽(numericValue), 16).
      4. Assert: The length of hex is 2.
      5. Set escaped to the string-concatenation of the code unit 0x005C (REVERSE SOLIDUS), "x", and hex.
    2. Else,
      1. Set escaped to the string-concatenation of escaped and EncodeForRegExpEscape(c).
  5. Return escaped.
 Note

Despite having similar names, EscapeRegExpPattern and RegExp.escape do not perform similar actions. The former escapes a pattern for representation as a string, while this function escapes a string for representation inside a pattern.

22.2.5.1.1 EncodeForRegExpEscape ( c )

The abstract operation EncodeForRegExpEscape takes argument c (a code point) and returns a String. It returns a string representing a Pattern for matching c. If c is white space or an ASCII punctuator, the returned value is an escape sequence. Otherwise, the returned value is a string representation of c itself. It performs the following steps when called:

  1. If c is matched by SyntaxCharacter or c is U+002F (SOLIDUS), then
    1. Return the string-concatenation of 0x005C (REVERSE SOLIDUS) and UTF16EncodeCodePoint(c).
  2. Else if c is the code point listed in some cell of the “Code Point” column of Table 63, then
    1. Return the string-concatenation of 0x005C (REVERSE SOLIDUS) and the string in the “ControlEscape” column of the row whose “Code Point” column contains c.
  3. Let otherPunctuators be the string-concatenation of ",-=<>#&!%:;@~'`" and the code unit 0x0022 (QUOTATION MARK).
  4. Let toEscape be StringToCodePoints(otherPunctuators).
  5. If toEscape contains c, c is matched by either WhiteSpace or LineTerminator, or c has the same numeric value as a leading surrogate or trailing surrogate, then
    1. Let cNum be the numeric value of c.
    2. If cNum ≤ 0xFF, then
      1. Let hex be Number::toString(𝔽(cNum), 16).
      2. Return the string-concatenation of the code unit 0x005C (REVERSE SOLIDUS), "x", and StringPad(hex, 2, "0", start).
    3. Let escaped be the empty String.
    4. Let codeUnits be UTF16EncodeCodePoint(c).
    5. For each code unit cu of codeUnits, do
      1. Set escaped to the string-concatenation of escaped and UnicodeEscape(cu).
    6. Return escaped.
  6. Return UTF16EncodeCodePoint(c).

A Copyright & Software License

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© 2024 Jordan Harband,Kevin Gibbons

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