name = 'out of you'
foo = function(){
this.name = 'xxoo';
}
foo.prototype.say = function(){
console.log(this.name);
}
f = new foo();
f.say(); // 這句會輸出xxoo
setTimeout(f.say, 500); // 這句會輸出out of you

setTimeout.call(foo(), f.say, 500)