了解本地范围 [英] Understanding Local Scope

问题描述

无论我怎么努力，我都无法改变'i'的价值......

I can't manage to change the value of 'i' no matter how hard I try...

我的代码如下：

function changeValue(){
    //neither 'var i=99;' or 'i=99;' interferes with the 'i' on myFunction
}

function myFunction(){
    var i;

    for(i=0;i<3;i++){
        alert(i);
        changeValue();
        alert(i);
    }
}

myFunction();

我的问题：如何更改'i'的值（在上MyFunction ）使用 changeValue 函数？

My question: How can I change the value of 'i' (on MyFunction) using the changeValue function?

另外：我非常需要阅读一些关于此的指南，可能有人给我一个好的链接？

Also: I badly need read some guides about this, could someone give me a link to a good one?

推荐答案

移动 changeValue（）与 i 相同的范围：

function myFunction(){
    var i;
    for(i=0;i<3;i++){     
        alert(i);     
        changeValue();     
        alert(i);     
    }
    function changeValue() { i = 99; }
}

或者，放 i 与相同的范围changeValue（）：

var i;
function changeValue() { i = 99; }
function myFunction(){   
    // var i; // don't define i here
    for(i=0;i<3;i++){     
        alert(i);     
        changeValue();     
        alert(i);     
    }     
}    

或者，您可以告诉 changeValue（） i 的值是什么，然后让它返回新值：

Alternatively, you can tell changeValue() what the value of i is, then have it return the new value:

function changeValue(i) {
    return i + 1;
}

然后：

i = changeValue(i);

编辑：说明范围：

var a = 0;  //  global scope - accessible everywhere via a
            //  unless overridden by a locally scoped a
            //  always accessible via window.a

function doSomething () {
    var a = 1;  //  local scope - you can still access window.a
    var b = 2;  //  local scope - accessible to child scopes, but not global scope

    function innerFunction () {
        var a = 3;  //  you no longer have access to the parent function's a variable
                    //  you can still access window.a
        var c = 4;  //  only accessible here (since no child scopes exist)

        alert(window.a);  //  0
        alert(a);         //  3
        alert(b);         //  2
        alert(c);         //  4
    }

    innerFunction();

    alert(window.a);  //  0
    alert(a);         //  1
    alert(b);         //  2
    alert(c);         //  undefined - unavailable in this scope
}

doSomething();

alert(window.a);  //  0
alert(a);         //  0
alert(b);         //  undefined - unavailable in this scope
alert(c);         //  undefined - unavailable in this scope

这篇关于了解本地范围的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！