Can I use res.send() node.js method inside the loop?

as first answer you can do something like.

app.get("/repeat/:word/:times", function(req, res){
    var word = req.params.word;
    var times = parseInt(req.params.times);
    for(var i = 1; i<= times; i++){
         word = ' ' + word;  
     }
   res.send(word);
});

if you want a streaming api the look this documentation server-send-events(sse)


No.

Look at the documentation:

Sends the HTTP response

You can't have multiple responses to a single request.


Build a single response body in a variable as you loop. Send it once the loop is finished.