karatelabs/karate · error · RangeError

Set-like object's size is negative

Error message

Set-like object's size is negative

What it means

SetRecord validation per the ES spec (ToIntegerOrInfinity then RangeError): a Set-like object's 'size' coerced to a negative number, which is invalid for set operations. Fix the object so its 'size' is a non-negative number.

Solutions

1. Fix the size computation so it is non-negative, or clamp: Math.max(0, size).
2. Use a real Set as the other argument.
3. Validate other.size >= 0 before calling.

Example fix

// before
const like = { size: computedSize, has, keys };
mySet.difference(like);
// after
const like = { size: Math.max(0, computedSize), has, keys };
mySet.difference(like);

if (Number(other?.size) < 0) throw new RangeError('size must be >= 0');

function hasNonNegativeSize(v) { return v !== null && typeof v === 'object' && Number.isFinite(Number(v.size)) && Number(v.size) >= 0; }

try { return mySet.difference(other); } catch (e) { if (String(e).includes('size is negative')) return mySet.difference(new Set()); throw e; }

When it happens

Trigger: set.difference({ size: -1, has: fn, keys: fn }); or a Set-like whose size getter computes a negative count.

Common situations: Custom Set-like wrappers computing size with an off-by-one or subtracting counts incorrectly; deserialized objects with negative size sentinels.

Understand the failure class

Background: "value must be between 0 and 1" / "out of range" / "must not be negative" errors: fixing range-validation failures across open-source libraries — this error's family across 42 libraries.

Related errors

• array index too large for dense storage:
• Cannot convert non-finite number to BigInt
• Cannot convert non-integer number to BigInt
• Constructor Set requires 'new'
• Invalid array length

AI-assisted analysis of karatelabs/karate@a22eb90246 (2026-09-12). Data as JSON: /api/errors/c6673298eba8bb4b. Report an issue: GitHub.

Appendix: source

Thrown at karate-js/src/main/java/io/karatelabs/js/JsSetPrototype.java:177

        if (!(other instanceof ObjectLike obj)) {
            throw JsErrorException.typeError("Set.prototype method called with non-object");
        }
        CoreContext cc = context instanceof CoreContext c ? c : null;
        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) {

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