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Wie kehrt man in JavaScript eine Zeichenkette an Ort und Stelle um?

Gefragt el 6 de Juni, 2009
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Wie kehrt man eine Zeichenkette in JavaScript an Ort und Stelle um, wenn sie an eine Funktion mit einer Rückgabeanweisung übergeben wird, ohne integrierte Funktionen zu verwenden ( .reverse() , .charAt() usw.)?

Gefragt el 6 de Juni, 2009 von Nicht registrierter Benutzer

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Avatar von Irwin

Sie dürfen also nicht .charAt() verwenden, um die Zeichen der Zeichenkette zu erhalten?

Kommentiert el 6 de Juni, 2009 von Irwin

192 Stimmen

Avatar von Crescent Fresh

Das können Sie nicht. JavaScript-Zeichenfolgen sind unveränderlich, was bedeutet, dass der Speicher, der ihnen zugewiesen ist, nicht beschrieben werden kann, was echte "In-Place"-Umkehrungen unmöglich macht.

Kommentiert el 6 de Juni, 2009 von Crescent Fresh

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Avatar von baudtack

Re: crescentfresh's Kommentar siehe stackoverflow.com/questions/51185/

Kommentiert el 6 de Juni, 2009 von baudtack
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3voto

MT0 avatar
MT0 Punkte 108686

UTF-8-Strings können haben:

  • Kombinationen von diakritischen Zeichen wie b die sich aus dem b Zeichen und eine Anhängerschaft ~ Diakritisches Zeichen, das durch die Unicode-Escape-Sequenz erzeugt wird \u0303 ;
  • Multi-Byte-Zeichen wie z.B. die durch die Multi-Byte-Unicode-Escape-Sequenz erzeugt wird \uD83C\uDFA5 und
  • Mehrere Zeichen können mit einem Null-Breiten-Verbindungszeichen kombiniert werden (durch die Unicode-Escape-Sequenz \u200D ). Zum Beispiel kann das Zeichen kann aus den einzelnen (Multi-Byte-)Emojis zusammengesetzt werden, dann aus einem Null-Breiten-Joiner, dann aus einem weiteren Null-Breiten-Joiner, so dass das gesamte 3-Personen-Zeichen aus 8 Bytes besteht ( \uD83D\uDC68\u200D\uD83D\uDC69\u200D\uD83D\uDC66 ).

Dadurch werden alle 3 Fälle umgekehrt und die Bytes in der richtigen Reihenfolge gehalten, so dass die Zeichen umgekehrt werden (anstatt die Bytes der Zeichenkette naiv umzukehren):

(function(){
  var isCombiningDiacritic = function( code )
  {
    return (0x0300 <= code && code <= 0x036F)  // Comb. Diacritical Marks
        || (0x1AB0 <= code && code <= 0x1AFF)  // Comb. Diacritical Marks Extended
        || (0x1DC0 <= code && code <= 0x1DFF)  // Comb. Diacritical Marks Supplement
        || (0x20D0 <= code && code <= 0x20FF)  // Comb. Diacritical Marks for Symbols
        || (0xFE20 <= code && code <= 0xFE2F); // Comb. Half Marks

  };

  String.prototype.reverse = function()
  {
    let output = "";

    for ( let i = this.length; i > 0; )
    {
      let width = 0;
      let has_zero_width_joiner = false;

      while( i > 0 && isCombiningDiacritic( this.charCodeAt(i-1) ) )
      {
        --i;
        width++;
      }

      do {
        --i;
        width++;

        if (
             i > 0
          && "\uDC00" <= this[i]   && this[i]   <= "\uDFFF"
          && "\uD800" <= this[i-1] && this[i-1] <= "\uDBFF"
        )
        {
          --i;
          width++;
        }
        has_zero_width_joiner = i > 0 && "\u200D" == this[i-1];
        if ( has_zero_width_joiner )
        {
          --i;
          width++;
        }
      }
      while( i > 0 && has_zero_width_joiner );

      output += this.substr( i, width );
    }

    return output;
  }
})();

// Tests
[
  'abcdefg',
  'ab\u0303c',
  'a\uD83C\uDFA5b',
  'a\uD83C\uDFA5b\uD83C\uDFA6c',
  'a\uD83C\uDFA5b\u0306c\uD83C\uDFA6d',
  'TO THE PONY', // copied from http://stackoverflow.com/a/1732454/1509264
  'What  is this?'
].forEach(
  function(str){ console.log( str + " -> " + str.reverse() ); }
);

Update

Der obige Code enthält einige der am häufigsten verwendeten kombinierten diakritischen Zeichen. Eine vollständigere Liste von kombinierenden diakritischen Zeichen (die in den obigen Code eingefügt werden können) ist:

var isCombiningDiacritic = function( code )
{
  return (0x0300 <= code && code <= 0x036F)
      || (0x0483 <= code && code <= 0x0489)
      || (0x0591 <= code && code <= 0x05BD)
      || (code == 0x05BF)
      || (0x05C1 <= code && code <= 0x05C2)
      || (0x05C4 <= code && code <= 0x05C5)
      || (code == 0x05C7)
      || (0x0610 <= code && code <= 0x061A)
      || (0x064B <= code && code <= 0x065F)
      || (code == 0x0670)
      || (0x06D6 <= code && code <= 0x06DC)
      || (0x06DF <= code && code <= 0x06E4)
      || (0x06E7 <= code && code <= 0x06E8)
      || (0x06EA <= code && code <= 0x06ED)
      || (code == 0x0711)
      || (0x0730 <= code && code <= 0x074A)
      || (0x07A6 <= code && code <= 0x07B0)
      || (0x07EB <= code && code <= 0x07F3)
      || (code == 0x07FD)
      || (0x0816 <= code && code <= 0x0819)
      || (0x081B <= code && code <= 0x0823)
      || (0x0825 <= code && code <= 0x0827)
      || (0x0829 <= code && code <= 0x082D)
      || (0x0859 <= code && code <= 0x085B)
      || (0x08D3 <= code && code <= 0x08E1)
      || (0x08E3 <= code && code <= 0x0902)
      || (code == 0x093A)
      || (code == 0x093C)
      || (0x0941 <= code && code <= 0x0948)
      || (code == 0x094D)
      || (0x0951 <= code && code <= 0x0957)
      || (0x0962 <= code && code <= 0x0963)
      || (code == 0x0981)
      || (code == 0x09BC)
      || (0x09C1 <= code && code <= 0x09C4)
      || (code == 0x09CD)
      || (0x09E2 <= code && code <= 0x09E3)
      || (0x09FE <= code && code <= 0x0A02)
      || (code == 0x0A3C)
      || (0x0A41 <= code && code <= 0x0A51)
      || (0x0A70 <= code && code <= 0x0A71)
      || (code == 0x0A75)
      || (0x0A81 <= code && code <= 0x0A82)
      || (code == 0x0ABC)
      || (0x0AC1 <= code && code <= 0x0AC8)
      || (code == 0x0ACD)
      || (0x0AE2 <= code && code <= 0x0AE3)
      || (0x0AFA <= code && code <= 0x0B01)
      || (code == 0x0B3C)
      || (code == 0x0B3F)
      || (0x0B41 <= code && code <= 0x0B44)
      || (0x0B4D <= code && code <= 0x0B56)
      || (0x0B62 <= code && code <= 0x0B63)
      || (code == 0x0B82)
      || (code == 0x0BC0)
      || (code == 0x0BCD)
      || (code == 0x0C00)
      || (code == 0x0C04)
      || (0x0C3E <= code && code <= 0x0C40)
      || (0x0C46 <= code && code <= 0x0C56)
      || (0x0C62 <= code && code <= 0x0C63)
      || (code == 0x0C81)
      || (code == 0x0CBC)
      || (0x0CCC <= code && code <= 0x0CCD)
      || (0x0CE2 <= code && code <= 0x0CE3)
      || (0x0D00 <= code && code <= 0x0D01)
      || (0x0D3B <= code && code <= 0x0D3C)
      || (0x0D41 <= code && code <= 0x0D44)
      || (code == 0x0D4D)
      || (0x0D62 <= code && code <= 0x0D63)
      || (code == 0x0DCA)
      || (0x0DD2 <= code && code <= 0x0DD6)
      || (code == 0x0E31)
      || (0x0E34 <= code && code <= 0x0E3A)
      || (0x0E47 <= code && code <= 0x0E4E)
      || (code == 0x0EB1)
      || (0x0EB4 <= code && code <= 0x0EBC)
      || (0x0EC8 <= code && code <= 0x0ECD)
      || (0x0F18 <= code && code <= 0x0F19)
      || (code == 0x0F35)
      || (code == 0x0F37)
      || (code == 0x0F39)
      || (0x0F71 <= code && code <= 0x0F7E)
      || (0x0F80 <= code && code <= 0x0F84)
      || (0x0F86 <= code && code <= 0x0F87)
      || (0x0F8D <= code && code <= 0x0FBC)
      || (code == 0x0FC6)
      || (0x102D <= code && code <= 0x1030)
      || (0x1032 <= code && code <= 0x1037)
      || (0x1039 <= code && code <= 0x103A)
      || (0x103D <= code && code <= 0x103E)
      || (0x1058 <= code && code <= 0x1059)
      || (0x105E <= code && code <= 0x1060)
      || (0x1071 <= code && code <= 0x1074)
      || (code == 0x1082)
      || (0x1085 <= code && code <= 0x1086)
      || (code == 0x108D)
      || (code == 0x109D)
      || (0x135D <= code && code <= 0x135F)
      || (0x1712 <= code && code <= 0x1714)
      || (0x1732 <= code && code <= 0x1734)
      || (0x1752 <= code && code <= 0x1753)
      || (0x1772 <= code && code <= 0x1773)
      || (x17B4 <= code && code <= 0x17B5)
      || (0x17B7 <= code && code <= 0x17BD)
      || (code == 0x17C6)
      || (0x17C9 <= code && code <= 0x17D3)
      || (code == 0x17DD)
      || (0x180B <= code && code <= 0x180D)
      || (0x1885 <= code && code <= 0x1886)
      || (code == 0x18A9)
      || (0x1920 <= code && code <= 0x1922)
      || (0x1927 <= code && code <= 0x1928)
      || (code == 0x1932)
      || (0x1939 <= code && code <= 0x193B)
      || (0x1A17 <= code && code <= 0x1A18)
      || (code == 0x1A1B)
      || (code == 0x1A56)
      || (0x1A58 <= code && code <= 0x1A60)
      || (code == 0x1A62)
      || (0x1A65 <= code && code <= 0x1A6C)
      || (0x1A73 <= code && code <= 0x1A7F)
      || (0x1AB0 <= code && code <= 0x1B03)
      || (code == 0x1B34)
      || (0x1B36 <= code && code <= 0x1B3A)
      || (code == 0x1B3C)
      || (code == 0x1B42)
      || (0x1B6B <= code && code <= 0x1B73)
      || (0x1B80 <= code && code <= 0x1B81)
      || (0x1BA2 <= code && code <= 0x1BA5)
      || (0x1BA8 <= code && code <= 0x1BA9)
      || (0x1BAB <= code && code <= 0x1BAD)
      || (code == 0x1BE6)
      || (0x1BE8 <= code && code <= 0x1BE9)
      || (code == 0x1BED)
      || (0x1BEF <= code && code <= 0x1BF1)
      || (0x1C2C <= code && code <= 0x1C33)
      || (0x1C36 <= code && code <= 0x1C37)
      || (0x1CD0 <= code && code <= 0x1CD2)
      || (0x1CD4 <= code && code <= 0x1CE0)
      || (0x1CE2 <= code && code <= 0x1CE8)
      || (code == 0x1CED)
      || (code == 0x1CF4)
      || (0x1CF8 <= code && code <= 0x1CF9)
      || (0x1DC0 <= code && code <= 0x1DFF)
      || (0x20D0 <= code && code <= 0x20F0)
      || (0x2CEF <= code && code <= 0x2CF1)
      || (code == 0x2D7F)
      || (0x2DE0 <= code && code <= 0x2DFF)
      || (0x302A <= code && code <= 0x302D)
      || (0x3099 <= code && code <= 0x309A)
      || (0xA66F <= code && code <= 0xA672)
      || (0xA674 <= code && code <= 0xA67D)
      || (0xA69E <= code && code <= 0xA69F)
      || (0xA6F0 <= code && code <= 0xA6F1)
      || (code == 0xA802)
      || (code == 0xA806)
      || (code == 0xA80B)
      || (0xA825 <= code && code <= 0xA826)
      || (0xA8C4 <= code && code <= 0xA8C5)
      || (0xA8E0 <= code && code <= 0xA8F1)
      || (code == 0xA8FF)
      || (0xA926 <= code && code <= 0xA92D)
      || (0xA947 <= code && code <= 0xA951)
      || (0xA980 <= code && code <= 0xA982)
      || (code == 0xA9B3)
      || (0xA9B6 <= code && code <= 0xA9B9)
      || (0xA9BC <= code && code <= 0xA9BD)
      || (code == 0xA9E5)
      || (0xAA29 <= code && code <= 0xAA2E)
      || (0xAA31 <= code && code <= 0xAA32)
      || (0xAA35 <= code && code <= 0xAA36)
      || (code == 0xAA43)
      || (code == 0xAA4C)
      || (code == 0xAA7C)
      || (code == 0xAAB0)
      || (0xAAB2 <= code && code <= 0xAAB4)
      || (0xAAB7 <= code && code <= 0xAAB8)
      || (0xAABE <= code && code <= 0xAABF)
      || (code == 0xAAC1)
      || (0xAAEC <= code && code <= 0xAAED)
      || (code == 0xAAF6)
      || (code == 0xABE5)
      || (code == 0xABE8)
      || (code == 0xABED)
      || (code == 0xFB1E)
      || (0xFE00 <= code && code <= 0xFE0F)
      || (0xFE20 <= code && code <= 0xFE2F)
      || (code == 0x101FD)
      || (code == 0x102E0)
      || (0x10376 <= code && code <= 0x1037A)
      || (0x10A01 <= code && code <= 0x10A0F)
      || (0x10A38 <= code && code <= 0x10A3F)
      || (0x10AE5 <= code && code <= 0x10AE6)
      || (0x10D24 <= code && code <= 0x10D27)
      || (0x10F46 <= code && code <= 0x10F50)
      || (code == 0x11001)
      || (0x11038 <= code && code <= 0x11046)
      || (0x1107F <= code && code <= 0x11081)
      || (0x110B3 <= code && code <= 0x110B6)
      || (0x110B9 <= code && code <= 0x110BA)
      || (0x11100 <= code && code <= 0x11102)
      || (0x11127 <= code && code <= 0x1112B)
      || (0x1112D <= code && code <= 0x11134)
      || (code == 0x11173)
      || (0x11180 <= code && code <= 0x11181)
      || (0x111B6 <= code && code <= 0x111BE)
      || (0x111C9 <= code && code <= 0x111CC)
      || (0x1122F <= code && code <= 0x11231)
      || (code == 0x11234)
      || (0x11236 <= code && code <= 0x11237)
      || (code == 0x1123E)
      || (code == 0x112DF)
      || (0x112E3 <= code && code <= 0x112EA)
      || (0x11300 <= code && code <= 0x11301)
      || (0x1133B <= code && code <= 0x1133C)
      || (code == 0x11340)
      || (0x11366 <= code && code <= 0x11374)
      || (0x11438 <= code && code <= 0x1143F)
      || (0x11442 <= code && code <= 0x11444)
      || (code == 0x11446)
      || (code == 0x1145E)
      || (0x114B3 <= code && code <= 0x114B8)
      || (code == 0x114BA)
      || (0x114BF <= code && code <= 0x114C0)
      || (0x114C2 <= code && code <= 0x114C3)
      || (0x115B2 <= code && code <= 0x115B5)
      || (0x115BC <= code && code <= 0x115BD)
      || (0x115BF <= code && code <= 0x115C0)
      || (0x115DC <= code && code <= 0x115DD)
      || (0x11633 <= code && code <= 0x1163A)
      || (code == 0x1163D)
      || (0x1163F <= code && code <= 0x11640)
      || (code == 0x116AB)
      || (code == 0x116AD)
      || (0x116B0 <= code && code <= 0x116B5)
      || (code == 0x116B7)
      || (0x1171D <= code && code <= 0x1171F)
      || (0x11722 <= code && code <= 0x11725)
      || (0x11727 <= code && code <= 0x1172B)
      || (0x1182F <= code && code <= 0x11837)
      || (0x11839 <= code && code <= 0x1183A)
      || (0x119D4 <= code && code <= 0x119DB)
      || (code == 0x119E0)
      || (0x11A01 <= code && code <= 0x11A06)
      || (0x11A09 <= code && code <= 0x11A0A)
      || (0x11A33 <= code && code <= 0x11A38)
      || (0x11A3B <= code && code <= 0x11A3E)
      || (code == 0x11A47)
      || (0x11A51 <= code && code <= 0x11A56)
      || (0x11A59 <= code && code <= 0x11A5B)
      || (0x11A8A <= code && code <= 0x11A96)
      || (0x11A98 <= code && code <= 0x11A99)
      || (0x11C30 <= code && code <= 0x11C3D)
      || (0x11C92 <= code && code <= 0x11CA7)
      || (0x11CAA <= code && code <= 0x11CB0)
      || (0x11CB2 <= code && code <= 0x11CB3)
      || (0x11CB5 <= code && code <= 0x11CB6)
      || (0x11D31 <= code && code <= 0x11D45)
      || (code == 0x11D47)
      || (0x11D90 <= code && code <= 0x11D91)
      || (code == 0x11D95)
      || (code == 0x11D97)
      || (0x11EF3 <= code && code <= 0x11EF4)
      || (0x16AF0 <= code && code <= 0x16AF4)
      || (0x16B30 <= code && code <= 0x16B36)
      || (code == 0x16F4F)
      || (0x16F8F <= code && code <= 0x16F92)
      || (0x1BC9D <= code && code <= 0x1BC9E)
      || (0x1D167 <= code && code <= 0x1D169)
      || (0x1D17B <= code && code <= 0x1D182)
      || (0x1D185 <= code && code <= 0x1D18B)
      || (0x1D1AA <= code && code <= 0x1D1AD)
      || (0x1D242 <= code && code <= 0x1D244)
      || (0x1DA00 <= code && code <= 0x1DA36)
      || (0x1DA3B <= code && code <= 0x1DA6C)
      || (code == 0x1DA75)
      || (code == 0x1DA84)
      || (0x1DA9B <= code && code <= 0x1E02A)
      || (0x1E130 <= code && code <= 0x1E136)
      || (0x1E2EC <= code && code <= 0x1E2EF)
      || (0x1E8D0 <= code && code <= 0x1E8D6)
      || (0x1E944 <= code && code <= 0x1E94A)
      || (0xE0100 <= code && code <= 0xE01EF);
};
Beantwortet el 9 de Januar, 2017 von MT0 (108686 Punkte )

2voto

Nicht registrierter Benutzer avatar
Nicht registrierter Benutzer Punkte 0 
function reverseString(string) {
    var reversedString = "";
    var stringLength = string.length - 1;
    for (var i = stringLength; i >= 0; i--) {
        reversedString += string[i];
    }
    return reversedString;
}
Beantwortet el 6 de Juni, 2009 von Nicht registrierter Benutzer (0 Punkte )

2voto

Dzenis H. avatar
Dzenis H. Punkte 5945

Umkehrung einer Zeichenkette mit integrierten Funktionen

function reverse(str) {
  // Use the split() method to return a new array
  //  Use the reverse() method to reverse the new created array
  // Use the join() method to join all elements of the array into a string
  return str.split("").reverse().join("");
}
console.log(reverse('hello'));

Umkehrung einer Zeichenkette ohne die Hilfsmittel

function reversedOf(str) {
  let newStr = '';
  for (let char of str) {
    newStr = char + newStr
    // 1st round: "h" + "" = h, 2nd round: "e" + "h" = "eh" ... etc. 
    // console.log(newStr);
  }
  return newStr;
}
console.log(reversedOf('hello'));
Beantwortet el 31 de Januar, 2020 von Dzenis H. (5945 Punkte )

2voto

Ramsy de Vos avatar
Ramsy de Vos Punkte 902

Strings selbst sind unveränderlich, aber Sie können mit dem folgenden Code leicht eine umgekehrte Kopie erstellen:

function reverseString(str) {

  var strArray = str.split("");
  strArray.reverse();

  var strReverse = strArray.join("");

  return strReverse;
}

reverseString("hello");
Beantwortet el 11 de Kann, 2016 von Ramsy de Vos (902 Punkte )

2voto

alejandro avatar
alejandro Punkte 2725 
//es6
//array.from
const reverseString = (string) => Array.from(string).reduce((a, e) => e + a);
//split
const reverseString = (string) => string.split('').reduce((a, e) => e + a); 

//split problem
"".split('')[0] === Array.from("")[0] // "" === "" => false
"".split('')[0] === Array.from("")[0] // "" === "" => false
Beantwortet el 1 de Kann, 2017 von alejandro (2725 Punkte )

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