function isNotEmpty(elem) {
    var str = elem.value; 
    if(str == null || str.length == 0) { 
        alert("Please fill in the required field."); 
        return false; 
    } else { 
        return true; 
    } 
}

function isInteger(elem) {
    var myVal = parseInt(elem.value);
    if ( isNaN(myVal) ) {
        alert('Please enter a numeric value');
        return false; 
    } else { 
        return true; 
    }
}

function isSmaller(elem_a, elem_b) {
    var a = parseInt(elem_a.value);
    var b = parseInt(elem_b.value);
    if ( a > b ) {
        alert("Please enter a smaller value."); 
        return false; 
    } else { 
        return true; 
    }
}

function isPositive(elem_a) {
    var a = parseInt(elem_a.value);
    if ( a < 1 ) {
        alert("Please enter a bigger value."); 
        return false; 
    } else { 
        return true; 
    }
}