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Regular Expressions

RegExp in SSJS — creation, flags, test, exec, and the source/global/lastIndex accessors, with the SFMC engine quirks for capture groups, lastIndex, ignoreCase, and multiline.

Regular expressions work in SSJS using the ES3/ES5 RegExp API. Literal and constructor syntax both work, and test, String.match, String.replace, and String.split behave as expected. A few accessors and exec’s capture-group / lastIndex behavior differ from the spec — those are flagged below.

Status legend

Icon Meaning
✅ Works Available and behaves as expected
⚠️ Partial Available but with a documented caveat or bug
❌ Missing Not available (or undefined) — use the workaround

Members

Member ES Status Notes
RegExp.prototype.test(string) ES3 ✅ Works Most reliable way to check for a match
RegExp.prototype.exec(string) ES3 ⚠️ Partial Full match result[0] works; capture groups result[1]+ are undefined and lastIndex does not advance
RegExp.prototype.source ES3 ✅ Works Pattern text without slashes or flags
RegExp.prototype.global ES3 ✅ Works true if the g flag was set
RegExp.prototype.lastIndex ES3 ⚠️ Partial Does not advance after exec() / test() with the g flag
RegExp.prototype.ignoreCase ES3 ❌ Missing undefined in SFMC — track the i flag yourself
RegExp.prototype.multiline ES3 ❌ Missing undefined in SFMC — track the m flag yourself

Creating RegExp

// Literal syntax (preferred)
var emailPattern = /^[^\s@]+@[^\s@]+\.[^\s@]+$/;
var digitsOnly   = /^\d+$/;
var noSpaces     = /\s/g;

// Constructor syntax (for dynamic patterns)
var fieldName = "email";
var dynamicPattern = new RegExp(fieldName + "=([^&]+)", "i");

Flags

Flag Meaning
g Global — find all matches, not just the first
i Case-insensitive
m Multiline — ^ and $ match line boundaries 
var text = "Hello World hello";

/hello/i.test(text);   // true (case-insensitive)
text.match(/hello/gi); // ["Hello", "hello"] (global + case-insensitive)

test

(ES3) — ✅ Works. Returns true if the pattern matches the string, false otherwise. This is the most reliable way to detect a match in SFMC.

var email = "jane@example.com";
var emailRe = /^[^\s@]+@[^\s@]+\.[^\s@]+$/;

if (emailRe.test(email)) {
    Write("Valid email");
} else {
    Write("Invalid email");
}

Platform.Function.IsEmailAddress() is usually more reliable than a custom regex for SFMC email validation.

exec

(ES3) — ⚠️ Partial. exec returns an array whose result[0] (full match) is correct, but capture groups result[1] and beyond are undefined, and lastIndex does not advance, so the usual while ((m = re.exec(str)) !== null) loop never terminates with the g flag. To collect all matches or read capture groups, use String.match instead.

// ❌ Do NOT do this — lastIndex never advances, this loops forever:
// var re = /[a-z]+(\d+)/g;
// while ((match = re.exec(text)) !== null) { ... }

// ✅ Collect all matches with String.match + the g flag:
var text = "foo123 bar456 baz789";
var matches = text.match(/[a-z]+\d+/g);
// ["foo123", "bar456", "baz789"]

// ✅ Read a single match's full text (result[0] is reliable):
var first = /[a-z]+\d+/.exec(text);
Write(first[0]);   // "foo123"
// first[1] is undefined in SFMC even though the pattern has a group

To extract capture groups reliably, match the non-global pattern with String.match:

var dateMatch = "2026-06-18".match(/(\d{4})-(\d{2})-(\d{2})/);
// dateMatch[1] = "2026", dateMatch[2] = "06", dateMatch[3] = "18"

source

(ES3) — ✅ Works. Returns the pattern text, excluding the surrounding slashes and any flags.

var re = /\d{4}-\d{2}-\d{2}/g;
re.source;   // "\\d{4}-\\d{2}-\\d{2}"

global

(ES3) — ✅ Works. true if the g flag was set on the RegExp, false otherwise.

/abc/g.global;   // true
/abc/.global;    // false

lastIndex

(ES3) — ⚠️ Partial. The property exists but does not advance after exec() / test() with the g flag, so it cannot be used to drive stateful iteration. Use String.match(/.../g) to get all matches in one call.

var re = /\d+/g;
re.exec("a1 b2 c3");
re.lastIndex;   // stays 0 in SFMC — does not advance

// Use String.match instead to get every match:
"a1 b2 c3".match(/\d+/g);   // ["1", "2", "3"]

ignoreCase

(ES3) — ❌ Missing. RegExp.prototype.ignoreCase is undefined in SFMC. If you need to know whether the i flag is active, track it yourself when you construct the RegExp.

// ignoreCase is undefined in SFMC — store the flag separately:
var caseInsensitive = true;
var re = caseInsensitive ? /hello/i : /hello/;

multiline

(ES3) — ❌ Missing. RegExp.prototype.multiline is undefined in SFMC. Track the m flag yourself when constructing the RegExp if you need to read it back.

// multiline is undefined in SFMC — store the flag separately:
var isMultiline = true;
var re = isMultiline ? /^line/m : /^line/;

Common Patterns

// Email validation (basic)
var isEmail = /^[^\s@]+@[^\s@]+\.[^\s@]+$/.test(email);

// Digits only
var isNumeric = /^\d+$/.test(value);

// Alphanumeric
var isAlphanumeric = /^[a-zA-Z0-9]+$/.test(value);

// UUID / GUID
var isGuid = /^[0-9a-f]{8}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{12}$/i.test(value);

// URL query parameter extraction
function getQueryParam(url, name) {
    var re = new RegExp("[?&]" + name + "=([^&]*)");
    var match = url.match(re);
    return match ? decodeURIComponent(match[1]) : null;
}

// Escape HTML special characters
function escapeHtml(str) {
    return str.replace(/&/g, "&")
              .replace(/</g, "&lt;")
              .replace(/>/g, "&gt;")
              .replace(/"/g, "&quot;")
              .replace(/'/g, "&#39;");
}

See Also

See Also