(JavaScript) Regular Expression Replace Capture Groups

See more Regular Expressions Examples

Note: Chilkat uses PCRE2. See PCRE2 Regular Expressions
Also see: PCRE2 Performance

Note: This example requires Chilkat v11.1.0 or greater.

Note

This example is intended for running within a Chilkat.Js embedded JavaScript engine. All Chilkat JavaScript examples require Chilkat v11.4.0 or greater.

var success = false;

var subject = "John Anders, +_+_+ Mary Robins $$$$";
var pattern = "(?<first>\\w+)\\s+(?<last>\\w+)";

var sb = new CkStringBuilder();
sb.Append(subject);

var json = new CkJsonObject();
json.EmitCompact = false;

var timeoutMs = 2000;
var numMatches = sb.RegexMatch(pattern,json,timeoutMs);
if (numMatches < 0) {
    // Probably an error in the regular expression.
    // Suggestion: Use AI to help create and/or diagnose regular expressions.
    console.log(sb.LastErrorText);
    return;
}

// Examine the matches:
console.log(json.Emit());

// There are 2 matches:

// {
//   "named": {
//     "first": 1,
//     "last": 2
//   },
//   "match": [
//     {
//       "group": [
//         {
//           "cap": "John Anders",
//           "idx": 0,
//           "len": 11
//         },
//         {
//           "cap": "John",
//           "idx": 0,
//           "len": 4
//         },
//         {
//           "cap": "Anders",
//           "idx": 5,
//           "len": 6
//         }
//       ]
//     },
//     {
//       "group": [
//         {
//           "cap": "Mary Robins",
//           "idx": 19,
//           "len": 11
//         },
//         {
//           "cap": "Mary",
//           "idx": 19,
//           "len": 4
//         },
//         {
//           "cap": "Robins",
//           "idx": 24,
//           "len": 6
//         }
//       ]
//     }
//   ]
// }

// To replace capture groups, write code to examine each capture group within
// each match, and provide a replacement string.
// Then call RegexReplace.

// For example, let's capitalize the first names, and add append "on" to the last name.
// After doing replacements, we should get:  JOHN Anderson, +_+_+ MARY Robinson $$$$

var firstNameIdx = json.IntOf("named.first");
var lastNameIdx = json.IntOf("named.last");

var sbTemp = new CkStringBuilder();

var i = 0;
numMatches = json.SizeOfArray("match");
while (i < numMatches) {

    json.I = i;

    // The replacement string for the first name will be all uppercase.
    json.J = firstNameIdx;
    sbTemp.Clear();
    json.StringOfSb("match[i].group[j].cap",sbTemp);
    sbTemp.ToUppercase();
    json.UpdateSb("match[i].group[j].rep",sbTemp);

    // Append "on" to the last name.
    json.J = lastNameIdx;
    sbTemp.Clear();
    json.StringOfSb("match[i].group[j].cap",sbTemp);
    sbTemp.Append("on");
    json.UpdateSb("match[i].group[j].rep",sbTemp);

    i = i+1;
}

// The JSON now has replacement strings:
console.log(json.Emit());

// {
//   "named": {
//     "first": 1,
//     "last": 2
//   },
//   "match": [
//     {
//       "group": [
//         {
//           "cap": "John Anders",
//           "idx": 0,
//           "len": 11
//         },
//         {
//           "cap": "John",
//           "idx": 0,
//           "len": 4,
//           "rep": "JOHN"
//         },
//         {
//           "cap": "Anders",
//           "idx": 5,
//           "len": 6,
//           "rep": "Anderson"
//         }
//       ]
//     },
//     {
//       "group": [
//         {
//           "cap": "Mary Robins",
//           "idx": 19,
//           "len": 11
//         },
//         {
//           "cap": "Mary",
//           "idx": 19,
//           "len": 4,
//           "rep": "MARY"
//         },
//         {
//           "cap": "Robins",
//           "idx": 24,
//           "len": 6,
//           "rep": "Robinson"
//         }
//       ]
//     }
//   ]
// }

// Call RegexReplace to update the StringBuilder with the replacements.
success = sb.RegexReplace(json);
if (success == false) {
    console.log(sb.LastErrorText);
    return;
}

console.log("Result after doing replacements:");
console.log(sb.GetAsString());

// Result after doing replacements:
// JOHN Anderson, +_+_+ MARY Robinson $$$$