sharepoint Getting library content types using the library name


function getContentTypes(site_url,name_of_the_library){
    var ctx = new SP.ClientContext(site_url);
    var web = ctx.get_web();
    list = web.get_lists().getByTitle(name_of_the_library);

    // You can include any property of the SP.ContentType object (sp.js), for this example we are just getting the name
    ctx.executeQueryAsync(onQuerySucceeded, onQueryFailed);

function onQuerySucceeded(sender, args) {
    // var list is the one that we used in function "getContentTypes"
    var contentTypesEnumerator = (list.get_contentTypes()).getEnumerator();

    while (contentTypesEnumerator.moveNext()) {
        var contentType = contentTypesEnumerator.get_current();

function onQueryFailed(sender, args) {
    alert('Request failed. ' + args.get_message() + '\n' + args.get_stackTrace());