var v = "global variable";
var method = function(){
writeHtml(this.v);
}
var Class2 = function(){
this.v = "object variable in instance of Class2";
this.method = function(){
writeHtml(this.v);
}
}
var Class3 = function(){
this.v = "object variable in instance of Class3";
this.method = function(){
writeHtml(this.v);
}
}
var obj2 = new Class2();
var obj3 = new Class3();
method(); //global variable
obj2.method(); //object variable in instance of Class2
obj3.method(); //object variable in instance of Class3
method.call(obj2); //object variable in instance of Class2
method.call(obj3); //object variable in instance of Class3
obj2.method.call(obj3); //object variable in instance of Class3
obj2.method.call(this); //global variable
obj3.method.call(obj2); //object variable in instance of Class2
obj3.method.call(this); //global variable
可以看到，使用call或apply可以将方法绑定到指定的上下文中。在全局环境中this指向的上下文为全局对象。