karatelabs/karate · error · SyntaxError

Invalid RegExp literal:

Error message

Invalid RegExp literal: 

What it means

A JsRegex built from a literal-style string must have the form /pattern/flags — it must start with '/' and contain at least one more '/' so a non-empty pattern region exists. If lastSlashIndex <= 0 (no closing slash, or only the leading slash), a SyntaxError 'Invalid RegExp literal: <text>' is thrown. This mirrors the browser behavior where malformed regex literals are syntax errors.

Solutions

1. Ensure the literal string has both opening and closing slashes: /pattern/flags
2. Check any code that slices/concatenates the literal for a dropped trailing slash
3. Escape literal '/' inside the pattern as \/ so it is not mistaken for the terminator, and verify lastIndexOf('/') > 0

Example fix

// before
JsRegex r = new JsRegex("/abc"); // missing closing slash
// after
JsRegex r = new JsRegex("/abc/"); // complete literal

function isValidRegexLiteral(s) { return typeof s === 'string' && s.startsWith('/') && s.lastIndexOf('/') > 0; }
if (!isValidRegexLiteral(src)) throw new Error('malformed regex literal: ' + src);

try {
  const re = new JsRegex(literal);
} catch (JsErrorException e) {
  if (String(e.getMessage()).startsWith('Invalid RegExp literal')) {
    throw new IllegalArgumentException('regex literal missing slashes: ' + literal);
  }
  throw e;
}

When it happens

Trigger: Passing strings like '/', '/flags' (no closing slash), or an unterminated literal that lost its trailing slash (e.g. from string slicing or config interpolation) to the JsRegex literal constructor.

Common situations: Building regex source strings by concatenation and dropping the closing slash; reading a pattern from config/env where the slash was escaped or stripped; hand-editing a regex literal and deleting the trailing '/'.

Related errors

• Invalid regular expression: /
• extract() needs three arguments: text, regex, group
• extractAll() needs three arguments: text, regex, group
• String.prototype.replaceAll called with a non-global RegExp…
• String.prototype.matchAll called with a non-global RegExp…

AI-assisted analysis of karatelabs/karate@a22eb90246 (2026-09-12). Data as JSON: /api/errors/07fda41f90ab9b14. Report an issue: GitHub.

Appendix: source

Thrown at karate-js/src/main/java/io/karatelabs/js/JsRegex.java:76

        lastIndex = 0;
    }

    // @@matchAll clones matching state — the iterator starts from the
    // receiver's current position without ever writing it back.
    int currentLastIndex() {
        return lastIndex;
    }

    JsRegex() {
        this("(?:)");
    }

    JsRegex(String literalText) {
        super(null, JsRegexPrototype.INSTANCE);
        if (literalText.startsWith("/")) {
            int lastSlashIndex = literalText.lastIndexOf('/');
            if (lastSlashIndex <= 0) {
                throw JsErrorException.syntaxError("Invalid RegExp literal: " + literalText);
            }
            // extract pattern and flags from the literal
            this.pattern = literalText.substring(1, lastSlashIndex);
            this.flags = lastSlashIndex < literalText.length() - 1
                    ? literalText.substring(lastSlashIndex + 1)
                    : "";
        } else {
            // string patterns without delimiters
            this.pattern = literalText;
            this.flags = "";
        }
        this.global = this.flags.contains("g");
        this.sticky = this.flags.contains("y");
        this.groupNames = extractGroupNames(this.pattern);
        int javaFlags = translateJsFlags(this.flags);
        try {
            // unescape js-specific regex syntax that differs from Java
            String javaPattern = translateJsRegexToJava(this.pattern);

View on GitHub (pinned to a22eb90246)