<form >
    <input id="find_txt" type='search' name='find'  /> 
     <input id="find_btn" type='button' value='Найти'   />
</form>

<script>
document.getElementById('find_txt').addEventListener('keydown', (ev) => {
        if (ev.keyCode === 13) {
            location.href  += "/" + encodeURI(document.getElementById('find_txt').value);
            ev.preventDefault()
        }

})
document.getElementById('find_btn').addEventListener('click', (ev) => {
            location.href  += "/" + encodeURI(document.getElementById('find_txt').value);
})
</script>