Register ajax action hook.

add-ajax-extended.php

<?php
/**
 * Register ajax action hook.
 *
 * When you have lots of ajax actions in your theme or plugin then
 * this utility function is going to be quite handy!
 * By default all actions are for logged in users.
 *
 * Usage:
 * add_ajax( 'get_infinity_posts', 'prefix_get_infinity_posts' ); // for logged in only
 * add_ajax( 'get_infinity_posts', 'prefix_get_infinity_posts', true ); // for both
 * add_ajax( 'get_infinity_posts', 'prefix_get_infinity_posts', true, false ); // for logged out only
 *
 * @param string $action
 * @param callable $callback
 * @param bool $nopriv
 * @param bool $priv
 *
 * @return void
 */
function add_ajax( $action, callable $callback, $nopriv = false, $priv = true ) {
	$prefix = '_action_prefix_'; // usualy this is going to be your plugin slug
  
	if ( $priv ) {
	  add_action( 'wp_ajax' . $prefix . $action, $callback );
	}
  
	if ( $nopriv ) {
	  add_action( 'wp_ajax_nopriv' . $prefix . $action, $callback );
	}
}

add-ajax-with-prefix.php

<?php
/**
 * Register ajax action hook.
 * 
 * When you have lots of ajax actions in your theme or plugin then
 * this utility function is going to be quite handy!
 *
 * @param string $action
 * @param callable $callback
 * @param bool $nopriv
 *
 * @return void
 */
function prefix_add_ajax( $action, $callback, $nopriv = false ) {
    $prefix = '_action_prefix_'; // usualy this is going to be your plugin slug

    add_action( 'wp_ajax' . $prefix . $action, $callback );

    if ( $nopriv ) {
        add_action( 'wp_ajax_nopriv' . $prefix . $action, $callback );
    }
}

add-ajax-with-safety.php

<?php
/**
 * Register ajax action hook.
 * 
 * When you have lots of ajax actions in your theme or plugin then
 * this utility function is going to be quite handy!
 *
 * @param string $action
 * @param callable $callback
 * @param bool $nopriv
 *
 * @return void
 */
if ( ! function_exists( 'add_ajax' ) {
    function add_ajax( $action, $callback, $nopriv = false ) {
        $prefix = '_action_prefix_'; // usualy this is going to be your plugin slug

        add_action( 'wp_ajax' . $prefix . $action, $callback );

        if ( $nopriv ) {
            add_action( 'wp_ajax_nopriv' . $prefix . $action, $callback );
        }
    }
}

add-ajax.php

<?php
/**
 * Register ajax action hook.
 * 
 * When you have lots of ajax actions in your theme or plugin then
 * this utility function is going to be quite handy!
 *
 * @param string $action
 * @param callable $callback
 * @param bool $nopriv
 *
 * @return void
 */
function add_ajax( $action, $callback, $nopriv = false ) {
    $prefix = '_action_prefix_'; // usualy this is going to be your plugin slug

    add_action( 'wp_ajax' . $prefix . $action, $callback );

    if ( $nopriv ) {
        add_action( 'wp_ajax_nopriv' . $prefix . $action, $callback );
    }
}

use-add-ajax.php

<?php

function prefix_get_infinity_posts() {
    // process and return the response
}

add_ajax( 'get_infinity_posts', 'prefix_get_infinity_posts', true );
// and this will do the following
// add_action( 'wp_ajax_prefix_get_infinity_posts', 'prefix_get_infinity_posts' );
// add_action( 'wp_ajax_nopriv_prefix_get_infinity_posts', 'prefix_get_infinity_posts' );