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javascript中的作用域scope介绍_javascript技巧

WBOY
Release： 2016-05-16 18:13:18
Original
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而在javascript中，变量的作用域是按函数来划分的——变量在某个函数范围内有效。比如：

复制代码 代码如下:

var f = false;
if(true) { var f = true; } //此时f位于if内，也就是块内，等价于还是全局范围内
alert(f) //所以，结果为true


再如下例：
复制代码 代码如下:

var f = false;
function test() {
　　var f = true; //这是函数内定义的变量，只在函数内部有效，函数执行完毕后，该变量将被释放
}
test();
alert(f) //结果为false，并没有因为test()的执行而改变



再有，在javascript中声明的全局变量都可以看作是window对象的一个属性，比如：
复制代码 代码如下:

var test = "this is a test";
alert(window.test == test) //结果为true

这正好验证了上边所说的全局变量也是window对象的属性

最后，我们来看
[code]
function test() {
　　f = false;
}
test();
alert(f) //结果为false
[html]

那么，如果在声明变量时，如果不添加var（隐式声明），也被看作了全局变量了，尽管它是定义在函数之内的。
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