bibliotheca-php/webclient/view/98/manageentry/field-text.html

<div class="field-row-stacked">
	<label for="<?php echo $field['identifier']; ?>"><?php echo $I18n->t($field['displayname']); ?>
		(<span id="<?php echo $field['identifier']; ?>_counter"><?php echo 128-strlen($TemplateData['editData'][$field['identifier']] ?? ''); ?></span>)
	</label>
	<input id="<?php echo $field['identifier']; ?>" type="text" autocomplete="off"
	   name="fdata[<?php echo $field['identifier']; ?>]"
	   value="<?php echo $TemplateData['editData'][$field['identifier']] ?? ''; ?>"
       maxlength="128"
	/>

	<?php if(isset($field['bulkedit'])) { ?>
	<select name="fdata[additionalEditOption][<?php echo $field['identifier']; ?>]">
		<option value=""><?php echo $I18n->t('manageentry.select.bulkedit'); ?></option>
		<option value="add"><?php echo $I18n->t('manageentry.select.bulkedit.add'); ?></option>
		<option value="replace"><?php echo $I18n->t('manageentry.select.bulkedit.replace'); ?></option>
		<option value="empty"><?php echo $I18n->t('manageentry.select.bulkedit.clear'); ?></option>
	</select>
	<?php } ?>
</div>

<script type="text/javascript">
{
	const inputElement = document.getElementById("<?php echo $field['identifier']; ?>");
	const inputCounter = document.getElementById("<?php echo $field['identifier']; ?>_counter");

	inputElement.addEventListener("input", event => {
		const target = event.currentTarget;
		const maxLength = target.getAttribute("maxlength");
		const currentLength = target.value.length;

		inputCounter.innerHTML = `${maxLength - currentLength}`;
	});
}
</script>