how use $.ajax method code example

Example 1: ajax call

$.ajax({
        url: "Url",
        dataType: "json",
        type: "Post",
        async: true,
        data: {"Key":value,"Key2":value2},
        success: function (data) {
                
        },
        error: function (xhr, exception, thrownError) {
            var msg = "";
            if (xhr.status === 0) {
                msg = "Not connect.\n Verify Network.";
            } else if (xhr.status == 404) {
                msg = "Requested page not found. [404]";
            } else if (xhr.status == 500) {
                msg = "Internal Server Error [500].";
            } else if (exception === "parsererror") {
                msg = "Requested JSON parse failed.";
            } else if (exception === "timeout") {
                msg = "Time out error.";
            } else if (exception === "abort") {
                msg = "Ajax request aborted.";
            } else {
                msg = "Error:" + xhr.status + " " + xhr.responseText;
            }
            if (callbackError) {
                callbackError(msg);
            }
           
        }
    });

Example 2: $.ajax example

class DB {
		private $host = 'localhost';
		private $user = 'root';
		private $password = '';
		private $db_name = 'library';
		public $conn;
		public function connect() {
			$this-> conn = new mysqli($this-> host, $this-> user, $this-> password, $this-> db_name);
					
			return $this -> conn;

		
	}

}