All Questions

I have always viewed recursive functions with a bad eye, and I have rejected them in favor of other options.

Why would I do this?:

foo(0);
function foo(cont){
  console.log(cont);
  cont++;
  if(cont<50){
    foo(cont);
  }
}

Being able to do this:

foo();
function foo(){
  for(let cont=0;cont<50;cont++){
    console.log(cont);
  }
}

I have searched for information, and I have found that recursive functions can be used to optimize Tail Call Optimization Recursion functional javascript

To which I do not find much sense, if in the previous snippets we simulate a larger loop for example: cont < 99999. It función recursivafails before reaching the end while he forcompletes it.

And on the other hand, if we simulate an infinite loop, the fordoes not do it while the función recursivadoes try and again gives an error.

When I try to make a request GET, POST, PUT, PATCH,DELETE from my Frontend I receive from the server

Request from another origin blocked: Same origin policy prevents reading remote resource at http://my_server/ (reason: missing CORS 'Access-Control-Allow-Origin' header).

I have also seen it in English something like:

"No 'Access-Control-Allow-Origin' header is present on the requested resource. Origin 'null' is therefore not allowed access."

I've researched WHAT CORS is and the W3C comments on this topic , and I understand what Cross-Origin Resource Sharing means , but I don't understand how it works.

How could I solve this in my WEBS applications?

Finally, I have noticed that my front-end applications generally make two requests, one of type OPTIONSand the common ones [ GET, POST, PUT, PATCH....] this is because

I do the tests with test-cors.org and it gives me the same error

I have a pagination that works correctly, even the filter to paginate more rows on the same page, that is to say that through the filter I can show 10 or 50 rows or more.

The small defect that the code has is that the page is reloaded, changing the number of rows that are displayed and the same thing happens in the pagination buttons.

This is my code, everything is working on the same page index2.php

<div id="wrapper">
    <div class="container">
        <div id="news-header" class="bootgrid-header container-fluid">
            <div class="row">
                <div class="col-sm-12 actionBar">
                    <div class="search-bar">
                        <input type="text" id="myInput" onkeyup="myFunction()" placeholder="What are you looking for?">
                    </div>
                    <div class="actions btn-group">
                        <?php
                            $select_quantity = '';
                            if (isset($_POST['amount_show'])) :
                                $select_quantity = $_POST['amount_show'];
                            endif;
                        ?>
                        <form method="post" action="<?php echo htmlspecialchars($_SERVER["PHP_SELF"]);?>">
                            <select id="amount_show" name="amount_show" onchange="this.form.submit()">
                                <option value="10" <?php if ($select_quantity==10) echo "selected"; ?>>10</option>
                                <option value="25" <?php if ($select_quantity==25) echo "selected"; ?>>25</option>
                                <option value="50" <?php if ($select_quantity==50) echo "selected"; ?>>50</option>
                                <option value="100" <?php if ($select_quantity==100) echo "selected"; ?>>100</option>
                            </select>
                        </form>
                    </div>
                </div>
            </div>
        </div>
        <?php
            if (isset($_GET['page'])) :
                $page = $_GET['page'] ?: '';
            else :
                $page = 1;
            endif;

            if (isset($_POST['amount_show'])) :
                $records_by_page = $_POST['amount_show'];
            else :
                $records_by_page = 10;
            endif;

            $localization_sql = ($page-1) * $records_by_page;

            $sql = "SELECT id,name,email
                    FROM users
                    ORDER BY id DESC LIMIT $localization_sql, $records_by_page";
            $stmt = $con->prepare($sql);
            $stmt->execute();
            $stmt->store_result();
            if ($stmt->num_rows>0) :

            echo '<table id="myTable" class="table table-condensed table-hover table-striped bootgrid-table">
            <thead>
                <tr>
                    <th>Id</th>
                    <th>Name</th>
                    <th>Email</th>
                    <th>Action</th>
                </tr>
            </thead>
            <tbody>';

            $stmt->bind_result($id,$name,$email);
            while ($stmt->fetch()) :
                echo '<tr>
                    <td>'.$id.'</td>
                    <td>'.$name.'</td>
                    <td>'.$email.'</td>
                    <td>Edit</td>
                </tr>';
            endwhile;
            echo '</tbody>';
            echo '</table>';
            $stmt->close();

    /**
    *
    * Botones ATRAS / SIGUIENTES
    *
    */

            $sql = "SELECT * FROM users";
            $stmt = $con->prepare($sql);
            $stmt->execute();
            $stmt->store_result();

            $BD_records = $stmt->num_rows;
            $stmt->close();
            $con->close();

            $total_page = ceil($BD_records / $records_by_page);
            $prev = $page - 1;
            $next = $page + 1;
            echo '<div class=pagination>
            <ul class="pagination">';
            if ($prev > 0) :
                echo "<li><a href='index2.php?page=1'><i class='icon-angle-double-arrow'></i></a></li>";
                echo "<li><a href='index2.php?page=$prev'><i class='icon-angle-left'></i></a></li>";
            endif;

            for ($i=1; $i<=$total_page; $i++) :
                if ($page==$i) :
                    echo "<li><a class=active>". $page . "</a></li>";
                else :
                    echo "<li><a href='index2.php?page=$i'>$i</a></li>";
                endif;
            endfor;


            if ($page < $total_page ) :
                echo "<li><a href='index2.php?page=$next'><i class='icon-angle-right'></i></a></li>";
                echo "<li><a href='index2.php?page=$total_page'><i class='icon-angle-double-right'></i></a></li>";
            endif;

            echo '</ul></div>';

            else :
                $stmt->close();
            endif;

        ?>
    </div>
</div>

I have made the following configurations due to the recommendations of JSON, which have been recommended to me.

ajax.php

if (isset($_GET['page'])) :
                $page = $_GET['page'] ?: '';
            else :
                $page = 1;
            endif;

            if (isset($_POST['amount_show'])) :
                $records_by_page = $_POST['amount_show'];
            else :
                $records_by_page = 10;
            endif;

$sql = "SELECT id,name,email
FROM users
ORDER BY id DESC LIMIT $localization_sql, $records_by_page";
$result = $con->query($sql);
$data_rows = array();
$result = $con->query($sql);
while($row = mysqli_fetch_assoc($result)) {
    $data_rows[] = $row;
}

echo json_encode($data_rows, JSON_PRETTY_PRINT);

I found an ajax code which I have called script.js, and throughajax

$(document).ready(function() {  
 $.ajax({
            type: "GET",
            url: "ajax.php",
            dataType: "json",
            success: function(data) {
                tableRows = '';
                for (let i = 0; i < data.length; i++) {
                    tableRows += `
                    <tr>
                        <td>${data[i].id}</td>
                        <td>${data[i].name}</td>
                        <td>${data[i].email}</td>
                        <td>Edit<td>
                    </tr>`;
                }
                $("#tbody-insert").html(tableRows);
            }
    });              
});

I display the data with no problem.

<script src="https://ajax.googleapis.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<script type="text/javascript" src="script.js"></script>
<table id="myTable" class="table table-condensed table-hover table-striped bootgrid-table">
    <thead>
        <tr>
            <th>Id</th>
            <th>Name</th>
            <th>Email</th>
            <th>Action</th>
        </tr>
    </thead>
    <tbody id="tbody-insert">

    </tbody>
</table>

Now my problem is, how to show pagination buttons and filter show more result row.

How do I have to send this information to ajax and display the sent information?

can you explain to me

I have been working with relational tables, but it turns out that there are 4 types of "actions" when the child row is deleted or updated and I don't know what it could mean, although I put CASCADE on all of them without really knowing their function.

They help me?

Playing around with Python, I have come across an error type takes 2 positional arguments but 3 were given. My method, which is inside a class, was of the form

def add(x, y):
    return x +y

I had just read the basic documentation on classes and was aware of the @classmethodand modifiers @staticmethod, which the documentation says are basically "syntactic sugar" . I also know that selfor clsare not reserved words, so it doesn't matter if my first parameter is called self, clsor x.

The error obtained makes me think that by default, the methods of a class are considered class methods (and the first argument is considered a reference to the class/instance) and if I want them to be static then I have to put the modifier, but not I've found nothing that explicitly states this in the documentation.

It may seem obvious, but for me it has been quite counterintuitive that if I declare

def saludar() :
   print("hola")

inside a class, the call will fail because the function has 0 parameters but we will try to pass one (implicit) with the call. Can someone confirm that methods are class defaults, as if they were annotated with @classmethod?