Source code for https://formidable-masterminds.com/add-data-attribute-to-any-input-field

count-chracters-jquery.js

<script>
jQuery(document).ready(function ($) {
    "use strict";
    
    $('#field_headb1, #field_headb2').on('keyup', function() {
        var characters = $(this).val().length,
		    target_elem = "frm_field_" + $(this).attr("data-target") + "_container";
        /* write the count to the element */
        $(target_elem).html( characters + ' characters');
    });		    
});
</script>

formidable-html-after.html

<div id="frm_field_[id]_container" class="frm_form_field form-field [required_class][error_class]">
    <label for="field_[key]" class="frm_primary_label">[field_name]
        <span class="frm_required">[required_label]</span>
    </label>
    [input data-target="118"]
    [if description]<div class="frm_description" id="frm_desc_field_[key]">[description]</div>[/if description]
    [if error]<div class="frm_error">[error]</div>[/if error]
</div>

formidable-html-before.html

<div id="frm_field_[id]_container" class="frm_form_field form-field [required_class][error_class]">
    <label for="field_[key]" class="frm_primary_label">[field_name]
        <span class="frm_required">[required_label]</span>
    </label>
    [input]
    [if description]<div class="frm_description" id="frm_desc_field_[key]">[description]</div>[/if description]
    [if error]<div class="frm_error">[error]</div>[/if error]
</div>

text-input-after.html

<div id="frm_field_104_container" class="frm_form_field form-field  frm_top_container frm_two_thirds frm_first">
    <label for="field_vg9ks" class="frm_primary_label">Encrypted String
        <span class="frm_required"></span>
    </label>
    <input type="text" id="field_vg9ks" name="item_meta[104]" value="" data-invmsg="Text is invalid" data-target="118" readonly="readonly" aria-describedby="frm_desc_field_vg9ks">
    <div class="frm_description" id="frm_desc_field_vg9ks">String Encrypted with AES-256-CBC Cipher Method</div>
</div>

text-input-before.html

<div id="frm_field_104_container" class="frm_form_field form-field  frm_top_container frm_two_thirds frm_first">
    <label for="field_vg9ks" class="frm_primary_label">Encrypted String
        <span class="frm_required"></span>
    </label>
    <input type="text" id="field_vg9ks" name="item_meta[104]" value="" data-invmsg="Text is invalid" readonly="readonly" aria-describedby="frm_desc_field_vg9ks">
    <div class="frm_description" id="frm_desc_field_vg9ks">String Encrypted with AES-256-CBC Cipher Method</div>
</div>