The addition of propene with HOCl proceeds via the addition of 

Cl⁺ in the first step

Since O is more electronegative than Cl, therefore, heterolytic fission of HO-Cl gives OH^- and Cl⁺. 

Since alkenes undergo electrophilic addition reactions, therefore, electrophile (Cl⁺) attacks first to generate a more stable carbocation which then undergoes nucleophilic attack by HO^- to give propylene chlorohydrin.