get(index) {
    if (index < 0 || index >= this.left.length + this.right.length) {
      throw new RangeError(
        'Cannot access index `' +
          index +
          '` in a splice buffer of size `' +
          (this.left.length + this.right.length) +
          '`'
      )
    }

    if (index < this.left.length) return this.left[index]
    return this.right[this.right.length - index + this.left.length - 1]
  }
Array access;
does not move the cursor.

@param {number} index
  Index.
@return {T}
  Item.