Method ensureUniqueItemVisual

src/data/SeriesData.ts:1212–1233

(idx: number, key: K)

     */
    // TODO: use key to save visual to reduce memory.
    ensureUniqueItemVisual<K extends keyof Visual>(idx: number, key: K): Visual[K] {
        const itemVisuals = this._itemVisuals;
        let itemVisual = itemVisuals[idx] as Visual;
        if (!itemVisual) {
            itemVisual = itemVisuals[idx] = {} as Visual;
        }
        let val = itemVisual[key];
        if (val == null) {
            val = this.getVisual(key);

            // TODO Performance?
            if (zrUtil.isArray(val)) {
                val = val.slice() as unknown as Visual[K];
            }
            else if (isObject(val)) {
                val = zrUtil.extend({}, val);
            }

            itemVisual[key] = val;
        }
        return val;
    }
    /**
     * Set visual property of single data item
     *