Ajax client and nodejs express server exchange json and text data

ajax_node_express_array_json_text.js

// ajax client
$(".download-selected-list").click( function() {
    $.ajax( {
        type: "post",
        url:'http://localhost:3000/ajax-mongo/downloadImagesZip',
        contentType: 'application/json',    // to server
        data: JSON.stringify({"arr":arrSelectedSrc}),
        dataType: 'text',                   // from server
        // dataType: 'binary',              // from server
        success: function(recvdata) {
            console.log("download zip...");
        },
        error: function(req,status,error) {
            console.log("code:"+req.status+"\n"+"message:"+req.responseText+"\n"+"error:"+error);
        }
    });
});


// node express server
router.post('/downloadImagesZip', function(req, res, next) {
    var urlArr = req.body.arr;
    console.log("length : " + urlArr.length);

    for(var i=0; i<urlArr.length; i++) {
        console.log(urlArr[i]);
    }

    res.end( "This is zip data" );
});