How to have PHP boolean FALSE to be output as FALSE only

Question

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transfer a Variable from php to js

This might seem trivial. I am setting a PHP variable's value as false. Then after some processing I am outputting some JavaScript variables in a script. This is the code

$a = true;
$b = false;
echo '<script type="text/javascript">
          var a = '.$a.';
          var b = '.$b.';
      </script>';

When the script finishes I get this output:

var a = 1;
var b = ;

So I get syntax error in JavaScript. Now the question is, how to have those values as true boolean values in JavaScript as well?

Intended output:

var a = true;
var b = false;

I don't want string like 'true' or 'false'...or 1 and 0, but boolean true and false only. Any help regarding this, also with some explanation as to why PHP behaves this way?

Look at the logic of JavaScript booleans http://www.quirksmode.org/js/boolean.html — Ron van der Heijden, Jul 25 '12 at 06:35
There are similiar questions on SO - http://stackoverflow.com/questions/4948663/php-get-bool-to-echo-false-when-false - http://stackoverflow.com/questions/2249235/is-there-a-way-to-get-true-false-values-from-a-boolean-in-php - http://stackoverflow.com/questions/11512705/print-false-in-php And all do the same by using strings instead. — sascha, Jul 25 '12 at 06:35

score 9 · Accepted Answer · answered Jul 25 '12 at 06:33

9

echo '<script type="text/javascript">
          var a = '.($a?"true":"false").';
          var b = '.($b?"true":"false").';
      </script>';

I suppose, You cant simply echo true/false to get the word, You need to convert it to string.

answered Jul 25 '12 at 06:33

dpitkevics

1,238
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1

right and when you echo it in js, the js value will hold a boolean, not a string because it won't echo with quotes around it – dano Jul 25 '12 at 06:35

score 4 · Answer 2 · answered Jul 25 '12 at 06:35

4

Use json_encode.

$a = true;
$b = false;
echo '<script type="text/javascript">
          var a = '.json_encode($a).';
          var b = '.json_encode($b).';
      </script>';

answered Jul 25 '12 at 06:35

xdazz

158,678
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score 3 · Answer 3 · answered Jul 25 '12 at 06:38

3

One more way to do it would be using var_export()

echo '<script type="text/javascript">
          var a = ', var_export($a), ';
          var b = ', var_export($b), ';
      </script>';

answered Jul 25 '12 at 06:38

Adi

5,089
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that's really interesting one, thanks – Shades88 Jul 25 '12 at 10:12

score 2 · Answer 4 · answered Jul 25 '12 at 06:36

2

Encode as JSON.

$ php
<?php
echo json_encode(true) . "\n";
echo json_encode(false) . "\n";             
true
false

answered Jul 25 '12 at 06:36

Ignacio Vazquez-Abrams

776,304
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score 1 · Answer 5 · answered Jul 25 '12 at 06:33

1

I suspect this would work and be easy to add:

($val ? "true" : "false")

answered Jul 25 '12 at 06:33

Marcus Johansson

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score 1 · Answer 6 · answered Jul 25 '12 at 06:36

I would use json_encode() on the php side, and JSON2 on the js side to transfer variables. (json2 is included in most js frameworks)

<?php
$js_vars = json_encode(array(
    'a' => true,
    'b' => false,
));
?>
<script>
   JS_VARS = JSON.parse('<?php print $js_vars?>');
   console.log(JS_VARS.a, JS_VARS.b);
</script>

Works for single variables too, but I would recommend to group your variables so they won't pollute the javascript's global object.

How to have PHP boolean FALSE to be output as FALSE only

6 Answers6