boolean variables posted through AJAX being treated as strings in server side

Question

Following is a part of an AJAX functionality to add classes and packs to session cart:-

The jquery part

function addClassToCart(itemId)
{
   addItemToCart(itemId,true);
}

function addPackToCart(itemId)
{
   addItemToCart(itemId,false);
}

function addItemToCart(itemId,isClass)
{   
     $.post(url+"/ajax/add_cart", { operation: 'add_cart','isClass':isClass, 'itemId': itemId},
        function(data)
        {
               if(data.success)
               {
                      alert("item added to cart");
               }
        }, "json");

}

The AJAX request processing php part -

//Checking operation and other posted parameters
if($_POST['isClass'])
{
  //Code to add class to session cart

}
else
{
  //Code to add pack to session cart
}

The strange thing

No matter whether I pass true/false (by calling addClassToCart() and addPackToCart()), always the code to add class to session cart executes.
If I put echo statements there like this:-

    if($_POST['isClass'])
    {
      echo "see if condition ".$_POST['isClass'];
    }
    else
    {
      echo "see else condition ".$_POST['isClass'];
    }

This is the output:-

addClassToCart() see if condition true
addPackToCart() see if condition false

Putting conditions like this in the jquery code however works fine:-

function addItemToCart(itemId,isClass)
 {  
     if(isClass)
        alert("is class");
     else
        alert("is pack");
 }

Finally, if I alter the server side code to this:-

if($_POST['isClass'] === true)
        {
          echo "see if condition ".$_POST['isClass'];
        }
        else
        {
          echo "see else condition ".$_POST['isClass'];
        }

These are the outputs -

addClassToCart() see else condition true
addPackToCart() see else condition false

So, why is the boolean variable treated as a string here? Am I doing something wrong in posting parameters?

Thanks, Sandeepan

Answer 1

You aren't doing anything wrong per se, it's just that when it gets posted, it looks like this:

operation=add_cart&isClass=true&itemId=1234

PHP can't tell what the data type is because it isn't passed, it's always just a string of POST data, so compare it to "true" to do your checks, like this:

if($_POST['isClass'] === "true")
{
  //Code to add class to session cart
}
else
{
  //Code to add pack to session cart
}

Answer 2

Also you can use filter_var function with filter FILTER_VALIDATE_BOOLEAN. According to php documentation it

Returns TRUE for "1", "true", "on" and "yes". Returns FALSE otherwise. If FILTER_NULL_ON_FAILURE is set, FALSE is returned only for "0", "false", "off", "no", and "", and NULL is returned for all non-boolean values.

So receiving of POST parameter will look like:

$isClass = filter_var ($_POST['isClass'], FILTER_VALIDATE_BOOLEAN);

Answer 3

This is a bit of an old question, but I'm surprised nobody has posted this here as solution.

Just use 1 and 0 instead of true and false when you're constructing your ajax requests. When you do a == comparison, they'll be interpreted as true/false.

JS:

$.ajax({
  url: '....',
  data: {
    foo: 1,
    bar: 0
  }
});

PHP:

<?php
  if ($_GET['foo']) {
     //...
  } else {
     //...
  }

  echo $_GET['bar'] ? 'bar is true' : 'bar is false';
?>

Answer 4

1. Send the data from your javascript as stringified JSON.
2. Make a PHP function to convert the strings 'true' and 'false' to boolean value.

Personally I like #2, which goes with Nick Craver's answer.