深入理解js中this的用法

function test() {  
  this.x = 1;  
  alert(x);
}

test();

var x = 1;
function test() {
  alert(this.x);
}
test();//1

var x = 1;
function test() {
  this.x = 0;
}
test();
alert(x);//0 

function test() {
  alert(this.x);
}

var o = {};
o.x = 1;
o.m = test;
o.m(); //1

function test() {  
   this.x = 1;
}
var o = new test();
alert(o.x);//1

var x = 0;
function test() {
  alert(this.x);
}

var o = {};
o.x = 1;
o.m = test;
o.m.apply(); //0
o.m.apply(o);//1