Sanitizer examples for customizer settings.

customizer_sanitizers.php

<?php

// Sanitize Select fields
function sanitize_select($input, $setting) {
    $input = sanitize_key($input);
    $choices = $setting->manager->get_control($setting->id)->choices;
    return (array_key_exists($input, $choices) ? $input : $setting->default);
}

// Sanitize Checkboxes
function sanitize_checkbox($input) {
    return ( ( isset( $input ) && true == $input ) ? true : false );
}

// Sanitize Range
function sanitize_range($input, $setting) {
	
	// Ensure input is an absolute integer
	$input = absint( $input );
	
	// Get the input attributes
	// associated with the setting
	$atts = $setting->manager->get_control( $setting->id )->input_attrs;
	
	// Get min 
	$min = ( isset( $atts['min'] ) ? $atts['min'] : $input );
	
	// Get max 
	$max = ( isset( $atts['max'] ) ? $atts['max'] : $input );
	
	// Get Step
	$step = ( isset( $atts['step'] ) ? $atts['step'] : 1 );
	
	// If the input is within the valid range, 
	// return it; otherwise, return the default
	return ( $min <= $input && $input <= $max && is_int( $input / $step ) ? $input : $setting->default );
}

// Sanitize Pages Dropdown
function sanitize_dropdown_pages($input, $setting)
{
    // Ensure $input is an absolute integer.
    $page_id = absint( $input );
  
    // If $page_id is an ID of a published page, return it; otherwise, return the default.
    return ( 'publish' == get_post_status( $page_id ) ? $page_id : $setting->default );
}