ajax within object, undefined

Edit: digged out some old code , added blue lines, explanation ?


comments = new Comments("some text")

function Comments(jsp)
{
this.jsp = jsp;
var that = this;
this.save = function(obj)
{
alert(this.jsp);// pops out 'some text'
....
///call ajax ... catch response in catch_save

}

this.catch_save = function()
{
if (xmlHttp.readyState==4 || xmlHttp.readyState=="complete")
{
alert(this.jsp);// pops out undefined
alert(that.jsp);// pops out 'some text' }
}


}



how come that there is undefined ?

this refers to the current object so its value is dependent on where it's used. catch_save isn't called with the new keyword so this refers to nothing. Obviously if you did var inst=new catch_save();, this would refer to inst, but that's not what you want...