How to correctly handle ajax timeouts

For example, a user want to login, the connection is slow or the request is stuck into some network , then the user waits, but sometimes is better resend the request than waiting.

Questions:

What would be the desirable waiting time? (no uploading files, just simple login) I've put 15 secs, but maybe it's too much.
What's the best solution?

1) Keep the user waiting till he decides to click login again

2) Set an ajax timeout

$.ajax({

url: '{{ url('/login') }}',
data: data,
method: 'POST',
timeout: 15000,

and display them an error

error: function(data, status, error){

if(status==="timeout") {
var errorString = 'Please retry. Ref Timeout';                      
}

3) do an auto retry (code)

$.ajax({
url : 'someurl',
type : 'POST',
data :  ....,   
tryCount : 0,
retryLimit : 3,
...
error: function(data, status, error){
    if (status == 'timeout') {
       this.tryCount++;
       if (this.tryCount <= this.retryLimit) {
       //try again
           $.ajax(this);
           return;
       }            
       return;
    }

4) Use a wrapper function over the ajax

setTimeout(function(){
    $.ajax({...})
}, 15000);

5) Some other options

Solution

You can do both, try 2 times and then fail:

$.ajax({
    url: '{{ url('/login') }}',
    data: data,
    method: 'POST',
    timeout: 5000, // Set timeout to 5000ms (5 seconds)
    retryCount: 0, // Number of retries, starts at 0
    retryLimit: 1, // The maximum number of retries
    success: function(data) {
        // do stuff
    },
    error: function(data, status, error) {
        if (status === "timeout") {
            this.retryCount++;
            if (this.retryCount <= this.retryLimit) {
                console.log("Retrying");
                $.ajax(this);
            } else {
                alert('Timeout');                       
            }
            return;
        }
        // Handle other errors...
    }
});