Including JavaScript in PHP function Error

Question

I had a weird problem here. Please check the code below. I do not understand how this code below is created by somehow part of it is working, considering mixture of php variables and javascript variables.

First, let us see what the alert() outputs (take note that $lat and $lng is different from the array $vlat):

In Line 8 of the code below, alert(eventlocation) properly displays the coordinates of the GoogleMap latlng (so the implementation is correct)
In Line 13, alert(s) was able to display incrementing values (i.e. 0,1,2,3,4,..) based on the for loop in the previous line so it is also correct.
In Line 14, alert($vlat[0]) was able to display the latitude of the first element of that array (declared before this set of codes) so it is also correct
In Line 15, alert($vlat[1]) was able to display the latitude of the second element of that array so it is also correct
But in Line 16, alert($vlat[s]) displayed undefined.

Can anyone explain that? Thanks

    echo "<script src= 'http://maps.google.com/maps?file=api&amp;v=2&amp;key=ABQIAAAA2jrOUq9ti9oUIF0sJ8it1RTNr3PHi_gURF0qglVLyOcNVSrAsRRu2C3WQApcfD0eh9NLdzf9My0b9w' type='text/javascript'> </script>
    <script language='javascript' type='text/javascript'>
    function getabc(){
        var eventlocation;
        var volunteerlocation;
        var s;
        eventlocation = new GLatLng($lat, $lng);
        //alert(eventlocation);
        var volunteerDist = new Array();
        s = $ctr;
        var tvid = new Array();
        for(s=0;s<$numrows;s++){
            //alert(s);
            //alert($vlat[0]);
            //alert($vlat[1]);
            //alert($vlat[s]);
        }
    }
    a = getabc();     < /script>";

$ctr is declared before this and it is initially set to 0 (zero) — Brandon Young
– Brandon Young, Commented Mar 15, 2012 at 9:37
what is $vlat set to? it looks like that variable doesn't contain anything at index s — jlb
– jlb, Commented Mar 15, 2012 at 9:39
@jlb $ctr is initially set to zero, s is set to variable $ctr mainly because for some reasons, using $ctr in the for loop gives an error — Brandon Young
– Brandon Young, Commented Mar 15, 2012 at 9:40
I believe the issue is you're accessing the PHP array $vlat (on the server side) with an index value only later defined in the JS part (on the client side). — user247702
– user247702, Commented Mar 15, 2012 at 9:41
Try print_r($vlat) before your echo statement to see what that variable contains. — Jeff
– Jeff, Commented Mar 15, 2012 at 9:41

user247702 · Accepted Answer · 2012-03-15 10:29:43Z

1

alert($vlat[0]);
alert($vlat[1]);
alert($vlat[s]);

$vlat[0], $vlat[1] and $vlat[s] are parsed on the server before they is sent to the client. The first two can be resolved, but PHP does not know what s is, since s is only defined once the client side is reached.

Edit from chat discussion

$json = json_encode($vlat);

echo "<script language='javascript' type='text/javascript'>
   function test(){
       var obj = JSON.parse('$json');
       alert(obj);
   }
   < /script>";

edited Mar 15, 2012 at 10:29

answered Mar 15, 2012 at 9:45

user247702

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5 Comments

user247702 Over a year ago

You can serialise the PHP array to JSON, so it can be accessed by the JavaScript. See stackoverflow.com/a/4885796/247702

Brandon Young Over a year ago

var obj = JSON.parse('<?php echo json_encode($vlat); ?>'); does not work.. there is an error

Brandon Young Over a year ago

it just does not show anything.. meaning there is an error.. the process stops after this line is called

user247702 Over a year ago

When you look at the source of the rendered page, what are you seeing in place of __THIS__ in var obj = JSON.parse('__THIS__');?

user247702 Over a year ago

let us continue this discussion in chat

Alexander van Oostenrijk · Accepted Answer · 2012-03-15 09:45:16Z

0

The variable s that you are using to index the PHP array vlat is a variable that you declared in JavaScript. You cannot use it to index a PHP array.

What your code tries to do is to have PHP access a JavaScript variable, which it cannot. You can have PHP echo JavaScript, yes, but it doesn't work both ways.

answered Mar 15, 2012 at 9:45

Alexander van Oostenrijk

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3 Comments

Brandon Young Over a year ago

so what do you suggest i should do?

totallyNotLizards Over a year ago

I'd suggest passing in $vlat as an object into javascript, and looping through it in pure JS rather than trying to access the PHP variable in your JS loop. Something like var myArray = <?php echo json_encode($vlat);?>; might work.

Brandon Young Over a year ago

var obj = <?php echo json_encode($vlat);?>; alert(obj); there is an error so alert() does not run;

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