All Questions

Most of us say, (often without really knowing),

"Do not use global variables"

Martin Fowler expresses in one of his books, Patterns of Enterprise Application Architecture , that

"any global variable is always guilty until proven otherwise"

• Why is it bad practice to use global variables?
• Are they really harmful?
• Or is it just an irrational prejudiced hatred on the part of the purists ?

Source: mundogeek.net - Global variables

Dynamic statements are SQL statements that are created as strings and in which values ​​obtained from some source (usually from the user) are inserted/concatenated, which can make them vulnerable to SQL injection if they are not sanitized. inputs, such as:

$id_usuario = $_POST["id"];

mysql_query("SELECT * FROM usuarios WHERE id = $id_usuario");

This is an example of a serious vulnerability in the security of an application (web or not) because if the user entered a value like 1; DROP TABLE usuarios;--this, we would find that the statement executed would be:

SELECT * FROM usuarios WHERE id = 1; DROP TABLE usuarios;--

And the Users table with all the data contained in it would be deleted.

How can I prevent SQL injection from happening in PHP?

I have always seen that JavaScriptthere is:

• assignments=
• comparisons ==and===

I understand that it ==does something similar to compare the value of the variable and ===it also compares the type (like a java equals).

Could someone confirm this point for me and extend it? . I'm a Javanese and sometimes I love javascript untyping and sometimes I hate it.

What is the correct way in javascript to compare undefined, nulland other default values?

variable == null
variable === null

Is undefinedit used as a text string or as a keyword? Which of the following comparisons is correct for an element htmlwithout value? (for example a label without content)

variable == "undefined"
variable === "undefined"
variable == undefined
variable === undefined

Ask

How to validate an e-mail that accepts all Latin characters?

• By Latin characters I mean accented letters, ñ, ç, and all those used by languages ​​like Spanish, Portuguese, Italian... Latin.

Context

• The goal is to display an icon next to the text as the user types their email address.
• I am not interested in accepting all valid cases. It was a design decision to cover only the most frequent emails. That is, letters (including accents and the like) and the symbols ._%+-.
• I can use code from other sources, as long as they are popular (eg jQuery).

Code

document.getElementById('email').addEventListener('input', function() {
    campo = event.target;
    valido = document.getElementById('emailOK');
        
    emailRegex = /^[-\w.%+]{1,64}@(?:[A-Z0-9-]{1,63}\.){1,125}[A-Z]{2,63}$/i;
    //Se muestra un texto a modo de ejemplo, luego va a ser un icono
    if (emailRegex.test(campo.value)) {
      valido.innerText = "válido";
    } else {
      valido.innerText = "incorrecto";
    }
});

<p>
    Email:
    <input id="email">
    <span id="emailOK"></span>
</p>

cases

I am using the regex

/^[-\w.%+]{1,64}@(?:[A-Z0-9-]{1,63}\.){1,125}[A-Z]{2,63}$/i

Which works perfect in cases like

[email protected]
[email protected]

But it fails with accents and other Latin letters

germá[email protected]
yo@mi-compañía.com
estaçã[email protected]

What is the difference between a innerand a outer join?

And what is the function of modifiers?

• left
• right
• full