Magento 2 - admin form show textbox on dropdown change

I have a form in admin with dropdown and textbox.

I want to show textbox only if dropdown value is set to yes.

I have not used UI-component for this.

I have tried below code but its not working.

<?php
namespace Company\Module\Block\Adminhtml\Syncpolicy\Edit\Tab;
class Listrules extends \Magento\Backend\Block\Widget\Form\Generic implements \Magento\Backend\Block\Widget\Tab\TabInterface
{
    /**
     * @var \Magento\Store\Model\System\Store
     */
    protected $_systemStore;

    protected $_resources;

    /**
     * @param \Magento\Backend\Block\Template\Context $context
     * @param \Magento\Framework\Registry $registry
     * @param \Magento\Framework\Data\FormFactory $formFactory
     * @param \Magento\Store\Model\System\Store $systemStore
     * @param array $data
     */
    public function __construct(
        \Magento\Backend\Block\Template\Context $context,
        \Magento\Framework\Registry $registry,
        \Magento\Framework\Data\FormFactory $formFactory,
        \Magento\Store\Model\System\Store $systemStore,
        array $data = array()
    ) {
        $this->_systemStore = $systemStore;
        parent::__construct($context, $registry, $formFactory, $data);
    }

    /**
     * Prepare form
     *
     * @return $this
     */
    protected function _prepareForm()
    {
        /* @var $model \Magento\Cms\Model\Page */
        $model = $this->_coreRegistry->registry('module_syncpolicy_format');
            $isElementDisabled = false;
        /** @var \Magento\Framework\Data\Form $form */
        $form = $this->_formFactory->create();
        $form->setHtmlIdPrefix('page_');

        $htmlIdPrefix = $form->getHtmlIdPrefix();

        $fieldset = $form->addFieldset('base_fieldset', array('legend' => __('Synchronization Policy')));
        if ($model->getId()) {
            $fieldset->addField('id', 'hidden', array('name' => 'id'));
        }


        $selectField = $fieldset->addField('select_field', 'select', array(
                'label' => 'Show/Hide Selection',
                'name' => 'select_field',           
                'values' => array(
                    array(
                        'value' => 1,
                        'label' => 'Yes',
                    ),
                    array(
                        'value' => 0,
                        'label' => 'No',
                    ),
                ),
                'onChange'  => 'showHideField()',
            ));


        $fieldset->addField('field_to_hide', text, array(
            'label'  => $this->__('Test'),
        ));


        $selectField->setAfterElementHtml('
                                <script>
                                function showHideField() {                                              
                                    $("field_to_hide").toggle()
                                }
                                </script>
                            ');


        $form->setValues($model->getData());
        $this->setForm($form);

        return parent::_prepareForm();   
    }

    /**
     * Prepare label for tab
     *
     * @return string
     */
    public function getTabLabel()
    {
        return __('List Rules');
    }

    /**
     * Prepare title for tab
     *
     * @return string
     */
    public function getTabTitle()
    {
        return __('List Rules');
    }

    /**
     * {@inheritdoc}
     */
    public function canShowTab()
    {
        return true;
    }

    /**
     * {@inheritdoc}
     */
    public function isHidden()
    {
        return false;
    }

    /**
     * Check permission for passed action
     *
     * @param string $resourceId
     * @return bool
     */
    protected function _isAllowedAction($resourceId)
    {
        return $this->_authorization->isAllowed($resourceId);
    }
}