Javascript - Stop form submit depending on ajax response [duplicate]

Answer 1

use e.preventDefault(); to prevent the form from submitting, and then use this.submit() (isn't calling the jQuery .submit() trigger function, but rather the native <form> .submit() function) to submit the form.

$("form").submit(function(e) {
            e.preventDefault();
            var tray = $('select[name=tray_id]').val();
            var form = this;
            $.ajax({
                type: "POST",
                url: "modules/reserve-check.php",
                data: {tray_id: tray},
                cache: false,
                complete : function(result){callback(result, form)}
            });       
        });

var callback = function(result, form){
  if(!result)
    form.submit();
};

Answer 2

As the ajax call is asynchronous, you have to prevent the form from submitting, and then when a result is returned, you check if it matches the condition and submit the form with the native submit handler, avoiding the preventDefault() in the jQuery event handler :

$("form").submit(function(e) {
    e.preventDefault();

    var self = this,
        tray = $('select[name=tray_id]').val();

    $.ajax({
        type: "POST",
        url: "modules/reserve-check.php",
        data: {tray_id: tray},
        cache: false
    }).done(function(result) {
        if (result == "") self.submit();
    }).fail(function() {
        alert('error');
    });
});