karatelabs/karate · error · RuntimeException

extract() needs three arguments: text, regex, group

Error message

extract() needs three arguments: text, regex, group

What it means

Karate's extract() JS utility applies a regex to text and returns one capture group from the first match. It requires exactly the trio text, regex, and group index; calling it with fewer than three arguments throws this error.

Solutions

1. Pass all three arguments: extract(text, 'pattern', 1)
2. Use group 0 if you want the whole match
3. If the regex itself is the problem, verify it compiles before blaming the argument count

Example fix

// before
var id = karate.extract(responseBody, 'id=(\\d+)');
// after
var id = karate.extract(responseBody, 'id=(\\d+)', 1);

if (text == null || regex == null || group == null) throw new Error('extract requires text, regex and group');

function canExtract(args) { return args.length >= 3 && typeof args[1] === 'string' && typeof args[2] === 'number'; }

try { id = karate.extract(text, regex, 1); } catch (e) { karate.log('extract failed: ' + e.message); }

When it happens

Trigger: Calling extract(text, regex) omitting the group index, extract(text) with only the text, or extract() with no arguments.

Common situations: Porting from other regex helpers that default to group 0; forgetting that group is 1-based here; trimming arguments while debugging.

Understand the failure class

Background: "missing required argument" and "the following required arguments were not provided": what required-argument errors mean and how to fix them — this error's family across 20 libraries.

Related errors

• extractAll() needs three arguments: text, regex, group
• eval() needs one argument
• expect() needs at least one argument
• append() needs at least two arguments
• appendTo() needs at least two arguments: list and item(s)

AI-assisted analysis of karatelabs/karate@a22eb90246 (2026-09-12). Data as JSON: /api/errors/294e2bdc07be3ef2. Report an issue: GitHub.

Appendix: source

Thrown at karate-core/src/main/java/io/karatelabs/core/KarateJsUtils.java:148

     * Usage: karate.distinct([1, 2, 2, 3, 1]) => [1, 2, 3]
     */
    static JavaInvokable distinct() {
        return args -> {
            if (args.length == 0 || args[0] == null) {
                return new ArrayList<>();
            }
            if (!(args[0] instanceof List<?> list)) {
                return new ArrayList<>();
            }
            Set<Object> seen = new LinkedHashSet<>(list);
            return new ArrayList<>(seen);
        };
    }

    static JavaInvokable extract() {
        return args -> {
            if (args.length < 3) {
                throw new RuntimeException("extract() needs three arguments: text, regex, group");
            }
            String text = args[0].toString();
            String regex = args[1].toString();
            int group = ((Number) args[2]).intValue();
            Pattern pattern = Pattern.compile(regex);
            Matcher matcher = pattern.matcher(text);
            if (!matcher.find()) {
                return null;
            }
            return matcher.group(group);
        };
    }

    static JavaInvokable extractAll() {
        return args -> {
            if (args.length < 3) {
                throw new RuntimeException("extractAll() needs three arguments: text, regex, group");
            }

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