Try This Below Code..
<?php
/**
* Copyright © 2016 Magento. All rights reserved.
* See COPYING.txt for license details.
*/
// @codingStandardsIgnoreFile
/**
* Product view template
*
* @see \Magento\Catalog\Block\Product\View\Description
*/
?>
<?php
$_helper = $this->helper('Magento\Catalog\Helper\Output');
$_product = $block->getProduct();
$_call = $block->getAtCall();
$_code = $block->getAtCode();
$_className = $block->getCssClass();
$_attributeLabel = $block->getAtLabel();
$_attributeType = $block->getAtType();
$_attributeAddAttribute = $block->getAddAttribute();
if ($_attributeLabel && $_attributeLabel == 'default') {
$_attributeLabel = $_product->getResource()->getAttribute($_code)->getFrontendLabel();
}
if ($_attributeType && $_attributeType == 'text') {
$_attributeValue = ($_helper->productAttribute($_product, $_product->$_call(), $_code)) ? $_product->getAttributeText($_code) : '';
} else {
$_attributeValue = $_helper->productAttribute($_product, $_product->$_call(), $_code);
}
?>
<?php if ($_attributeValue): ?>
<?php if($_code === 'short_description') { ?>
<div class="value more" <?php /* @escapeNotVerified */ echo $_attributeAddAttribute;?> >
<?php if ($_product->getData('short_description')) {
$string = strip_tags($_product->getData('description'));
if (strlen($string) > 50) {
// truncate string
$stringCut = substr($string, 0, 50);
$string = substr($stringCut, 0, strrpos($stringCut, ' ')).'... <a href="javascript:void(0);" class="readmore">Read More</a>';
}
echo $string;
?>
<?php
}else {?>
<?php /* @escapeNotVerified */ echo $_attributeValue;
}
?>
</div>
<div class="less" style="display:none">
<?php echo $_attributeValue; ?>
<a href="javascript:void(0);" class="readless">Read Less</a>
</div>
<script type="text/javascript">
console.log('test');
require(["jquery"],function($){
$('.readmore').on("click",function(){
$('.less').show();
$('.more').hide();
});
$('.readless').on("click",function(){
$('.less').hide();
$('.more').show();
});
});
</script>
<?php } else { ?>
<div class="product attribute <?php /* @escapeNotVerified */ echo $_className?>">
<?php if ($_attributeLabel != 'none'): ?><strong class="type"><?php /* @escapeNotVerified */ echo $_attributeLabel?></strong><?php endif; ?>
<div class="value" <?php /* @escapeNotVerified */ echo $_attributeAddAttribute;?>><?php /* @escapeNotVerified */ echo $_attributeValue; ?></div>
</div>
<?php } ?>
<?php endif; ?>