karatelabs/karate · error · JsErrorException

Iterator value is not an entry object

Error message

Iterator value {entry} is not an entry object

What it means

When `new Map(iterable)` consumes an iterable, each yielded value must be an entry object (a List/array of [key, value] or an object with 0/1 properties). Karate throws this TypeError when an iterator yields something else — a scalar, a function, etc. — so no key/value pair can be extracted.

Solutions

1. Wrap each element as a [key, value] pair: `new Map([[1,'a'],[2,'b']])`
2. Use `Object.entries(obj)` instead of `Object.keys(obj)` when building a Map from an object
3. Log or inspect the iterable before passing to new Map() to confirm each element is a 2-element array or entry object
4. Filter/map the iterable first if the source data has heterogeneous shapes

Example fix

// before
const m = new Map([1, 2, 3]); // TypeError
// after
const m = new Map([[1, null], [2, null], [3, null]]); // or [1,2,3].map(k => [k, k*2])

// every element must be a pair
if (!arr.every(e => Array.isArray(e) && e.length >= 1)) {
  throw new Error('iterable for new Map() must yield [key, value] entries');
}

function isEntry(e) { return Array.isArray(e) || (e !== null && typeof e === 'object'); }

try {
  const m = new Map(iterable);
} catch (e) {
  if (String(e.message).includes('is not an entry object')) {
    throw new Error('bad input to new Map: ' + e.message);
  } else throw e;
}

When it happens

Trigger: `new Map([1, 2, 3])` — iterator yields numbers, not pairs; `new Map('ab')` — each char is a string; `new Map(gen())` where the generator yields non-entry values; a nested array flattened by mistake so inner items are scalars.

Common situations: Hand-writing arrays of keys instead of [key, value] pairs; converting an Object to Map via Object.keys (yields strings) instead of Object.entries; porting JS from environments where 2-element arrays were accidentally flattened.

Understand the failure class

Background: "Invalid ... format", "must be in format X", "does not look like a ..." — invalid argument format errors across CLI tools and libraries — this error's family across 17 libraries.

Related errors

• NoSuchElementException
• Result of the Symbol.iterator method is not an object
• iterator result is not an object
• The iterator does not provide a 'throw' method
• iterator.throw is not a function

AI-assisted analysis of karatelabs/karate@a22eb90246 (2026-09-12). Data as JSON: /api/errors/505f876bd65cdec0. Report an issue: GitHub.

Appendix: source

Thrown at karate-js/src/main/java/io/karatelabs/js/JsMapConstructor.java:81

        }
        JsMap map = new JsMap();
        if (args.length == 0 || args[0] == null || args[0] == Terms.UNDEFINED) {
            return map;
        }
        // Look up `set` on the freshly-constructed map's prototype chain — honors
        // user-overridden Map.prototype.set per spec 24.1.1.1 step 9.
        Object setFn = map.getMember("set");
        if (!(setFn instanceof JsCallable adder)) {
            throw JsErrorException.typeError("Map.prototype.set is not callable");
        }
        JsIterator iter = IterUtils.getIterator(args[0], context);
        CoreContext cc = context instanceof CoreContext c ? c : null;
        Object savedThis = cc != null ? cc.thisObject : null;
        try {
            while (iter.hasNext()) {
                Object entry = iter.next();
                if (!(entry instanceof List) && !(entry instanceof ObjectLike)) {
                    throw JsErrorException.typeError("Iterator value " + entry + " is not an entry object");
                }
                Object k;
                Object v;
                if (entry instanceof List<?> list) {
                    k = list.isEmpty() ? Terms.UNDEFINED : list.get(0);
                    v = list.size() < 2 ? Terms.UNDEFINED : list.get(1);
                } else {
                    ObjectLike ol = (ObjectLike) entry;
                    k = ol.getMember("0");
                    v = ol.getMember("1");
                    if (k == null) k = Terms.UNDEFINED;
                    if (v == null) v = Terms.UNDEFINED;
                }
                if (cc != null) cc.thisObject = map;
                adder.call(context, new Object[]{k, v});
                if (cc != null && cc.isError()) {
                    return map;
                }

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