if condition with Javascript inside PHP

Question

It is possible to check if the variable is null in the JS section in PHP?

<?php
print("<SCRIPT language=javascript> 

            string_patr = \"$string_patr\";
            string_seri = \"$string_seri\";
            if(string_patr == null){
                vv_patr = string_seri;
            }
            else{
                vv_patr = string_patr+','+ string_seri;
            }
            alert(vv_patr);


        </SCRIPT>");


?>

Answer 1

Check on the PHP side

Based on the code present in the question, the simplest is to check with PHP the contents of the variables, thus preparing the value to be used by Javascript on the client side:

if (is_null($string_patr)) {
    $vv_patr = $string_seri;
}
else {
    $vv_patr = $string_patr.','.$string_seri;
}

echo '
<script type="text/javascript">
  var vv_patr = "'.$vv_patr.'";
  alert(vv_patr);
</script>';

Example in Ideone.

This way PHP checks the variables and when is to send the Javascript code to the browser, will less code and already ready to be used.

Learn more about the function is_null() php.

---

Check on the Javascript side

To keep your code logical on the Javascript side, you will need to change the way you check the contents of the variable.

The null in the PHP variable will be reflected in nothingness in the Javascript variable.

$string_patr = null;
$string_seri = "bubu";

print("<SCRIPT language=javascript>
string_patr = \"$string_patr\";
string_seri = \"$string_seri\";
if(string_patr == null){
vv_patr = string_seri;
}
else{
vv_patr = string_patr+','+ string_seri;
}
alert(vv_patr); 
</SCRIPT>");

Will result in:

<SCRIPT language=javascript> 
    string_patr = "";
    string_seri = "bubu";
    if(string_patr == null){
        vv_patr = string_seri;
    }
    else{
        vv_patr = string_patr+','+ string_seri;
    }
    alert(vv_patr);
</SCRIPT>

Notice that the null on the PHP side turned out to be nothingness on the Javascript side. Since you have double quotes, you end up with string_patr = ""; which allows you to change the check to:

 if ((!string_patr || string_patr.length === 0) {
    vv_patr = string_seri;
 }
 else {
    vv_patr = string_patr+','+ string_seri;
 }

So we’re seeing if the variable actually exists and it’s not empty.

Note: The type of check depends on what is expected to be in the variable, in the above suggested check you are checking whether it is null, undefined or empty.

Answer 2

Try it like this:

<?php
    echo "<SCRIPT> 
                string_patr = ".$string_patr.";
                string_seri = ".$string_seri.";
                if(string_patr == null){
                    vv_patr = string_seri;
                }
                else{
                    vv_patr = string_patr+','+ string_seri;
                }
                alert(vv_patr);
    </SCRIPT>";
?>

Answer 3

<script language=javascript> 

   function isNullCustom(test) 
   {
       return (test == null || test == "null" || typeof(test) == "undefined" || test == "");
   }

   var string_patr = "<?php echo $string_patr; ?>";
   var string_seri = "<?php echo $string_seri; ?>";

   if(isNullCustom(string_patr))
   {
      vv_patr = string_seri;
   }
   else
   {
      vv_patr = string_patr+','+string_seri;
   }

   alert(vv_patr);

</script>

I believe the problem is not in php. When you print null in a javascript variable, it is not a boleano value, but a string with the text 'null'.

I created a custom function to identify possible null cases for what you want.

Where, a variable that is found as:

• boleana null;
• string null;
• empty string (0 characters);
• or with its indefinite type;

Shall be null and void.

See if it works.