delete(key) {
    if (this.doc !== null) {
      transact(this.doc, transaction => {
        typeMapDelete(transaction, this, key);
      });
    } else {
      /** @type {Map<string, any>} */
      this._prelimContent.delete(key);
    }
  }
Remove a specified element from this YMap.

@param {string} key The key of the element to remove.