csom javascript get Document Libraries

I need to filter result to particular content types fo document library. I cannot seem to retrieve the content type of library. How is this possible. When I try with oList.get_contentTypes() object object is being returned.

function retrieveAllListProperties() {


    var clientContext = new SP.ClientContext();
    var oWebsite = clientContext.get_web();
    this.collList = oWebsite.get_lists();
    clientContext.load(collList);

    clientContext.executeQueryAsync(
        Function.createDelegate(this, this.onQuerySucceeded), 
        Function.createDelegate(this, this.onQueryFailed)
    );
}

function onQuerySucceeded() {
    var listInfo = '';
    var listEnumerator = collList.getEnumerator();

    while (listEnumerator.moveNext()) {
        var oList = listEnumerator.get_current();
        listInfo += 'Title: ' + oList.get_title()  + oList.get_contentTypes() + '\n';
    }
    alert(listInfo);
}