Send arrays of data from PHP to JavaScript

You'll want to use json_encode on the data, like

<?php
$arr=array('cow'=>'black','feet'=>4);
$encoded=json_encode($arr);

$encoded is now {"cow":"black","feet":4}, which JavaScript can work with. To send this to a page do

header('Content-Type: application/json');  
echo $encoded;

header has to happen before you output anything to the page, even a space or blank line, or PHP will give an error.

After generating the data as a PHP array, to output it to JS on the initial page load, you can print it out as the following. Not you don't need to output a special header in this case; it's part of your normal text/html document. The header is for an Ajax return.

<?php
$json_data=json_encode($your_array);
?>
<script>
   var an_obj=<?php echo $json_data;?>;
</script> 

Use datatype:"json" for data and datatype:"script" to set the data type for your ajax calls.

On the servers side set content-types to application/json and application/javascript , respectively.