var tehnoUser = 'Челмедведосвин'
tehno_user = document.querySelector('[name="claim"]')
tehno_user.value = tehnoUser
Partial support in IE8 is due to being limited to CSS 2.1 selectors and a small subset of CSS 3 selectors (see notes there). Additionally, it will have trouble with selectors including unrecognized tags (for example HTML5 ones).