karatelabs/karate · error · TypeError

Set-like object's 'has' is not callable

Error message

Set-like object's 'has' is not callable

What it means

While constructing a SetRecord from a Set-like object, its `has` member was not callable. The spec requires the Set-like to expose callable has and keys methods for difference/intersection to probe membership.

Solutions

1. Provide a callable has member on the Set-like object.
2. Use a real Set, which always has callable has/keys.
3. Verify Object.keys(other) includes 'has' and typeof other.has === 'function' before calling.

Example fix

// before
const like = { size: 1, keys: () => ['a'][Symbol.iterator]() };
mySet.difference(like);
// after
const like = { size: 1, has: k => k === 'a', keys: () => ['a'][Symbol.iterator]() };
mySet.difference(like);

if (typeof other?.has !== 'function' || typeof other?.keys !== 'function') throw new TypeError('Set-like must have callable has and keys');

function isCallableSetLike(v) { return v !== null && typeof v === 'object' && typeof v.has === 'function' && typeof v.keys === 'function'; }

try { return mySet.difference(other); } catch (e) { if (String(e).includes("'has' is not callable")) return mySet.difference(new Set()); throw e; }

When it happens

Trigger: set.difference({ size: 2, has: true, keys: fn }); or the Set-like is missing `has` entirely (undefined).

Common situations: Partially implemented Set-like objects (size and keys present, has forgotten); property name typos (e.g. `contains` instead of `has`); passing a plain Map (which has no `has`-as-own-member semantics the caller expects in that shape).

Understand the failure class

Background: "Must be a positive integer", "Invalid value", "Unsupported": the invalid-argument-value error family, when a library rejects the value you pass — this error's family across 35 libraries.

Related errors

• Set-like object's size is not a number
• Constructor Set requires 'new'
• Method Set.prototype called on incompatible receiver
• NoSuchElementException
• Set-like object's 'keys' is not callable

AI-assisted analysis of karatelabs/karate@a22eb90246 (2026-09-12). Data as JSON: /api/errors/dc70f5e9b5d85201. Report an issue: GitHub.

Appendix: source

Thrown at karate-js/src/main/java/io/karatelabs/js/JsSetPrototype.java:181

        Object rawSize = obj.getMember("size", obj, cc);
        Number numSize = Terms.toNumberCoerce(rawSize, cc);
        double d = numSize.doubleValue();
        if (Double.isNaN(d)) {
            throw JsErrorException.typeError("Set-like object's size is not a number");
        }
        // ToIntegerOrInfinity, then RangeError on negative — spec step 7.
        long intSize;
        if (Double.isInfinite(d)) {
            intSize = d > 0 ? Long.MAX_VALUE : Long.MIN_VALUE;
        } else {
            intSize = (long) d;
        }
        if (intSize < 0) {
            throw JsErrorException.rangeError("Set-like object's size is negative");
        }
        Object hasFn = obj.getMember("has", obj, cc);
        if (!(hasFn instanceof JsCallable has)) {
            throw JsErrorException.typeError("Set-like object's 'has' is not callable");
        }
        Object keysFn = obj.getMember("keys", obj, cc);
        if (!(keysFn instanceof JsCallable keys)) {
            throw JsErrorException.typeError("Set-like object's 'keys' is not callable");
        }
        return new SetRecord(obj, intSize, has, keys);
    }

    private static JsIterator keysIter(SetRecord rec, Context ctx) {
        return IterUtils.iteratorFromCallable(rec.keys, rec.setObj, ctx);
    }

    /** Spec normalize: -0 → +0 on values pulled from a foreign keys() iteration. */
    private static Object normalize(Object v) {
        return JsMap.normalizeKey(v);
    }

    /** Direct-populate a JsSet, bypassing Set.prototype.add per spec. */

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