How can I achieve that chapters do not start on a new page? Below you find a small example document, where I would like that the titles are all in one page. Thanks a lot for your time and help.
\documentclass[a4paper, 11pt, oneside]{book}
\makeatletter
\makeatother
\usepackage[a4paper,left=3cm,right=3cm,top=3cm,bottom=3cm]{geometry}
\usepackage{titlesec}
\titleformat{\chapter}{\bfseries \centering \sffamily}{\huge \Roman{chapter}.}{10pt}{\huge}
\begin{document}
\chapter{title1}
\chapter{title2}
\chapter{title3}
\end{document}
