function foot(){ this.add = function(x,y){ return x+y; ...
单项选择题
function foot(){ this.add = function(x,y){ return x+y; }}foot.prototype.add = function(x,y){ return x+y+10;}Object.prototype.substract = function(x,y){ return x-y;}var f1 = new foot();alert(f1.add(1,2));alert(f1.substract(1,2));
弹出结果是()