var DivOneClassArr = new Array();  
var DivTwoClassArr = new Array();  
  
function getElementsByClassName( ClassName1, ClassName2, obj ) {  
    if ( obj.className == ClassName1 ) {  
        DivOneClassArr[DivOneClassArr.length] = obj;  
    }  
    if ( obj.className == ClassName2 ) {  
        DivTwoClassArr[DivTwoClassArr.length] = obj;  
    }  
    for ( var i = 0; i < obj.childNodes.length; i++ )  
        getElementsByClassName( ClassName1, ClassName2, obj.childNodes[i] );  
}  
  
function fixHeight() {  
    DivOneClassArr.length = 0;  
    DivTwoClassArr.length = 0;  
    getElementsByClassName( 'main', 'sidebar', document.body );  
    for ( var i = 0; i < DivOneClassArr.length || i < DivTwoClassArr.length; i++ ) {  
        if(DivOneClassArr[i].offsetHeight > DivTwoClassArr[i].offsetHeight) {  
            DivTwoClassArr[i].style.height = DivOneClassArr[i].offsetHeight +'px';  
        }  
        else if (DivOneClassArr[i].offsetHeight < DivTwoClassArr[i].offsetHeight) {  
            DivOneClassArr[i].style.height = DivTwoClassArr[i].offsetHeight +'px';  
        }  
    }  
}