Method has

packages/joint-core/src/mvc/Data.mjs:7–10

(obj, key)

    }

    has(obj, key) {
        if (key === undefined) return this.map.has(obj);
        return key in this.map.get(obj);
    }

    create(obj) {
        if (!this.has(obj)) this.map.set(obj, Object.create(null));