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

Solution 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
}

Solution 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);

Solution 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';
?>

Solution 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.

View more solutions

Comments

[Sandeepan Nath]

So is there no other way around? I prefer doing boolean checks as much as possible.

[Nick Craver]

@sandeepan - nope, not sure what else to say other than...this is how http gets and posts work, it's perfectly normal.

[Gary]

Why not instead use '==' and let it do type conversion for you?

[Nick Craver]

@Gary - Because it's a string , "false" is still true because it's a non-zero length string...be explicit and you won't get surprises. The same rules apply to JavaScript for example, some people never use == and only use === for good reason.

[Gary]

I guess I had a misconception of type conversion. Thanks Nick.

[Hayden Chambers]

number 1 works far better when the object you want to save is multi-leveled.. no ugly recursive php functions required just json_decode

[mcrumley]

+1 for filter_var, one of the often overlooked parts of the PHP.

[Spock]

Beautiful! Validating a boolean like it were a string is imho ugly and fubar.

[r3wt]

you can type cast it to a boolean like so $foo = (bool) $_POST['foo'];

[Spencer Williams]

@r3wt You would need to explicitly test for 'true' and 'false' and reset those values to booleans. The string 'false' cast as a boolean will be true. Check out us2.php.net/manual/en/language.types.boolean.php to review how PHP converts such values.

[Jonathon Philip Chambers]

Although I voted up the top three answers this was the one that was so clean and elegant, it made it into my code. Well done.

[Lizesh Shakya]

The best solution for retrieving the data in Ajax or Api.

[Hashim Aziz]

Please get rid of the space between filter_var and its parentheses, it makes the code only slightly harder to read but unimaginably disrupting to my internal peace and the system won't let me make such a minor edit. 😬

[Tamara]

@HashimAziz done! Hope it brought internal peace to you :)

[Hashim Aziz]

@Tamara If only, but close enough. Haha thanks

[Boolean_Type]

In case if $_POST['isClass'] hasn't been passed at all (ie $_POST['isClass'] is NULL), filter_var($_POST['isClass'], FILTER_VALIDATE_BOOLEAN); will return false as well.