WordPress customizer range control with indicator for selected value. http://w3guy.com/wordpress-customizer-range-control-selected-indicator/

range-control.js

(function ($) {
    $(document).ready(function ($) {
        $('input[data-input-type]').on('input change', function () {
            var val = $(this).val();
            $(this).prev('.cs-range-value').html(val);
            $(this).val(val);
        });
    })
})(jQuery);

WP_Customize_Range_Control.php

<?php

class WP_Customize_Range_Control extends WP_Customize_Control
{
    public $type = 'custom_range';

    public function enqueue()
    {
        wp_enqueue_script(
            'cs-range-control',
            'path/to/range-control.js',
            array('jquery'),
            false,
            true
        );
    }

    public function render_content()
    {
        ?>
        <label>
            <?php if ( ! empty( $this->label )) : ?>
                <span class="customize-control-title"><?php echo esc_html($this->label); ?></span>
            <?php endif; ?>
            <div class="cs-range-value"><?php echo esc_attr($this->value()); ?></div>
            <input data-input-type="range" type="range" <?php $this->input_attrs(); ?> value="<?php echo esc_attr($this->value()); ?>" <?php $this->link(); ?> />
            <?php if ( ! empty( $this->description )) : ?>
                <span class="description customize-control-description"><?php echo $this->description; ?></span>
            <?php endif; ?>
        </label>
        <?php
    }
}

invalid value error on wp ?