var compare_plans = 0;
var field_clean = 0;

function invertCheckbox(field){
    
    checkboxes = document.getElementsByName(field);
        
    for (i=0; i<checkboxes.length; i++){
        
        checkboxes[i].checked = !checkboxes[i].checked;
        
    }
    
}

function toggle_compare(field){
    
    var compare_button_main = document.getElementById("compare");
    var compare_button = document.getElementById(field);
    
    if (compare_button.style.visibility == "hidden" || compare_button.style.visibility == ""){
        compare_button.style.visibility = "visible";
        
        compare_plans++;
        compare_button_main.disabled = false;
        compare_button_main.value="Compare: "+compare_plans;
    } else {
        compare_button.style.visibility = "hidden";
        
        compare_plans--;
        if (compare_plans == 0){
    	  compare_button_main.disabled = true;
    	  compare_button_main.value="Compare";
    	} else compare_button_main.value="Compare: "+compare_plans;
    }
}

function clr(field){
    if (field_clean == 0){
	field.value = '';
	field_clean = 1;
    }
}