Detecting EU DST

dst.js

function dstBounds(date, month) {
          var d = new Date(date.getFullYear(),/*March*/(month-1),31),
            day = d.getDay();                
        
        if (day != 0) d.setDate(d.getDate()-day);
        
        //Dst starts @(UTC 01:00) 
        //this implementation is in UTC+1 (02:00)
        d.setHours(2);    
         
    return d;

}

function isDst(date) {
    var start = dstBounds(date, 3),
        end = dstBounds(date,10);        
    
    if (date >= start && date <= end) return true;

    return false;
}

function equals(a,b, desc) {
    if (a!=b) throw new Error(a + ', ' +  b + ' are not equal at test: ' + desc)
}

function test() {

   //Test sundays dstBounds
     var year = 1970;
    
    while(year < 2100) {
        
        var d = new Date(year,1,1);
        var dststart = dstBounds(d, 3);
        var dstend = dstBounds(d, 10);
        
        if(dststart.getDay() != 0) console.log("Start not a sunday");
        if(dstend.getDay() != 0) console.log("End not a sunday");
                 
        year++;
    }
    
    //Test 2011 DST starts
    
    var d = new Date(2011, 2, 25);      
    var t = equals(isDst(d), false);
    
    var d = new Date(2011, 2, 27, 1,00);  
    var t = equals(isDst(d), false);
    
    var d = new Date(2011, 2, 27, 1,59);      
    var t = equals(isDst(d), false);
    
    var d = new Date(2011, 2, 27, 2,0);      
    var t = equals(isDst(d), true);
    
    var d = new Date(2011, 2, 27, 2,1);      
    var t = equals(isDst(d), true);
    
    
    var d = new Date(2011, 2, 28);
    var t = equals(isDst(d), true);
    
    
    //DST ends
    var d = new Date(2011, 9, 30);
    var t = equals(isDst(d), true);

    
    var d = new Date(2011, 9, 30, 1,00);
    var t = equals(isDst(d), true);

    
    
     var d = new Date(2011, 9, 30, 1,59);
    var t = equals(isDst(d), true);

    
    var d = new Date(2011, 9, 30, 2,00);
    var t = equals(isDst(d), true);

    
     var d = new Date(2011, 9, 30, 2,01);
    var t = equals(isDst(d), false);

    
    //2012 DST starts   
    
    var d = new Date(2012, 2, 23);      
    var t = equals(isDst(d), false, '2012 3 23');
    
    var d = new Date(2012, 2, 25, 1,00);  
    var t = equals(isDst(d), false, '2012, 3 25 01.00');
    
    var d = new Date(2012, 2, 25, 1,59);      
    var t = equals(isDst(d), false);
    
    var d = new Date(2012, 2, 25, 2,0);      
    var t = equals(isDst(d), true);
    
    var d = new Date(2012, 2, 26, 2,1);      
    var t = equals(isDst(d), true);
    
    
    var d = new Date(2012, 2, 27);
    var t = equals(isDst(d), true);
    
    //2012 DST Ends
     var d = new Date(2012, 9, 27);
    var t = equals(isDst(d), true);

    
    var d = new Date(2012, 9, 28, 1,00);
    var t = equals(isDst(d), true);

    
    
     var d = new Date(2012, 9, 28, 1,59);
    var t = equals(isDst(d), true);

    
    var d = new Date(2012, 9, 28, 2,00);
    var t = equals(isDst(d), true);

    
     var d = new Date(2012, 9, 28, 2,01);
    var t = equals(isDst(d), false);
    
    console.log("All OK");
};


test();