JSFiddle - React, Tailwind, and code Playground

HTML

<form class="custom-form ptForm" action="" method="POST" data-valid="true" data-loc="ru" data-xhr="true" data-final="">
                            <fieldset>
                                <div class="input-row input-row_required">
                                    <label class="input-row__label" for="fieldName">Название компании</label>
                                    <input class="input-row__text inputText" type="text" name="fieldName" value="" id="fieldName" size="45" tabindex="1">
                                </div>
                            </fieldset>
                            <fieldset>
                                <div class="input-row input-row_required">
                                    <label class="input-row__label" for="fieldEmail">Email</label>
                                    <input class="input-row__text inputText" type="email" name="fieldEmail" value="" id="fieldEmail" size="45" tabindex="2"">
                                </div>
                            </fieldset>
                        </form>

JavaScript

var values = document.querySelectorAll('.inputText')

values.forEach(function(value){
	value.addEventListener('blur', function(e) {
    e.target.value = e.target.value.trim();
    e.target.setAttribute('value', e.target.value.trim());
  });
});