声明两个同名变量 [英] Declaring two variable with the same name

问题描述

是否可以调用在函数外设置的同名变量?

Is it possible to call the same name variables which set outside of the function?

var a = $(window).width(); // I want to call this variable
if(!$.isFunction(p)){
    var a = $(window).height(); // Not this one
    alert(a);
}

FIDDLE

推荐答案

在像您这样的代码片段中，变量 a 正在被重新定义.这是因为 if 语句不会为变量创建另一个作用域.但是，函数可以.

In a code snippet such as yours, the variable a is being redefined. This is because an if statement doesn't create another scope for variables. However, functions do.

在这种情况下:

var a = 0; // global
function doStuff() {
    var a = 10; // local
    alert(a);
    alert(window.a)
}
alert(a);
doStuff();
alert(a);

在函数doStuff 中，变量a 被重新定义.因此，此剪辑将提醒数字 0、10、0、0.这证明全局变量没有在函数内部重新定义，因为在调用doStuff后打印a并不会改变a的值全局范围.

inside the function doStuff, the variable a is being redefined. This snipped will therefore alert the numbers 0, 10, 0, 0. This proves that the global variable is not redefined inside the function, as printing a after calling doStuff doesn't change the value of a in the global scope.

可以访问函数外部的变量 a，因为任何未在非全局范围内声明的变量都放置在 window 对象内.但是，如果使用此代码段(调用匿名函数，创建新范围):

The variable a outside of the function can be accessed, as any variable not declared in a non-global scope is placed inside the window object. However, if using this snippet (which calls an anonymous function, creating a new scope):

var a = 0; // global
function doStuff() {
    var a = 10; // local
    alert(a);
    alert(window.a)
    function() {
        var a = 20; // even more local
        alert(a);
        alert(window.a);
    }();
}
alert(a);
doStuff();
alert(a);

您不能在 doStuff 函数中访问 a 的值.您仍然可以使用 window.a 访问全局变量.

you cannot access the value of a inside the doStuff function. You can still access the global variable using window.a.

但是，在您的情况下，if 语句不会创建新范围，因此您将变量 a 重新定义为新值 $(window).height().

In your case, however, the if statement does not create a new scope, therefore you are redefining the variable a to the new value $(window).height().

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