How to check if I am inside the WP Theme Customizer preview?

Question

I have some elements showing on the home page that I do not want to display in the Theme Customizer preview window. Is there a simple check in PHP that I can use for that ?

For example:

<img class="background" src="<?php echo $background ?>" <?php if(is_wpThemeCustomizer()) echo 'style="display:none"' ?>/>

I could do it in javascript using the js file that is enqueued only in this case, but I would like to use PHP, or even better : CSS. Is it possible ?

Answer 1

Check for global variable $wp_customize:

if ( empty ( $GLOBALS['wp_customize'] ) ) 
{
    // show something
}

Update: in WordPress 4.0, you can use is_customize_preview().

Answer 2

Alternatively

global $wp_customize;
if (isset($wp_customize)) {
     // do stuff
}

Answer 3

From Wordpress 4.0 you can use is_customize_preview();

Answer 4

AS shared by iki, here is a simple example to add something conditionally, if currently on customizer preview page:

if (is_customize_preview()) {
    // perform customizer specific action
} else {
    // perform separate action
}