Is Ajax in WordPress

Question

Is there anyway to detect if the current server operation is currently an AJAX request in WordPress?

For example:

is_ajax()

Answer 1

Update: since WordPress 4.7.0 you can call a function wp_doing_ajax(). This is preferable because plugins that "do Ajax" differently can filter to turn a "false" into a "true".

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Original answer:

If you're using Ajax as recommended in the codex, then you can test for the DOING_AJAX constant:

if (defined('DOING_AJAX') && DOING_AJAX) { /* it's an Ajax call */ }