How can I transfer a PHP variable to JavaScript via Ajax?

Other Questions JavaScript
1

Ajax error occurs when JSON is expected from PHP output. Below is a sample PHP snippet and a JavaScript Ajax call using different variable names. How can I fix JSON parsing?

<?php
include 'config.php';
$result = pg_query("SELECT colX, colY FROM sample_table");
$output = '[';
while ($record = pg_fetch_assoc($result)) {
    $output .= '{"key":"' . $record['colX'] . '","num":' . $record['colY'] . '},';
}
$output .= ']';
echo $output;
?>

$.ajax({
  url: 'server_handler.php',
  method: 'GET',
  dataType: 'json',
  success: function(response) { console.log(response); },
  error: function() { alert('Ajax failed'); }
});
2

Based on personal experience, the error likely stems from improperly built JSON. In the provided code, an extra comma is added at the end of the JSON output, which can cause parsing errors in JavaScript. Using PHP’s json_encode function to output your data is a more reliable approach as it ensures the JSON is correctly formatted. It is also important to check that the Ajax call accurately expects this JSON format. Adjusting these details should resolve the transfer issue.

3

Another aspect to check is ensuring that PHP outputs exactly what is expected without any extraneous characters. Experience taught me that even a stray whitespace or a PHP notice printed before the intended JSON output can lead to a JSON parse error on the client side. It is advisable to set the correct content type in PHP with header(‘Content-Type: application/json’) to mitigate any issues. Using json_encode not only helps format the data correctly but also prevents errors associated with manual string concatenation.