<input type="text" id="search_cat" placeholder="Введите номер">
<input type="button" value="Перейти" onclick="subm_cat();">
<script>
function subm_cat() {
if ($('#search_cat').val().length == 0) {} else {
location.href = '/board/1-1-0-'+$('#search_cat').val();
}
}
</script>

<input type="text" id="search_cat" placeholder="Введите номер">  
<input type="button" value="Перейти" onclick="subm_cat();">  
<script>  
function subm_cat() {  
if ($('#search_cat').val().length == 0) {} else {  
location.href = '/board/1-1-0-'+$("#search_cat").val();  
}  
}  
</script>  

<script>    
function subm_cat() {    
if ($.trim($('#search_cat').val()).length > 0 ) {
location.href = '/board/1-1-0-'+$("#search_cat").val();    
}    
}    
</script>