在jQuery.post中，如何获取函数外部变量的值? [英] In jQuery.post, how do I get value of variable outside function?

问题描述

我具有以下功能:

var id = "10";
var type = "Type A";
var img = "myimage.jpg";

jQuery.post("my/path/somefile.php", { instance: 'getUrl', ID : id, type: type},
function(data)
{ 
    jQuery('#logo').attr("src",data.url + img);
},"json"); 

1. 在函数内部时如何获取img的值?
2. 如何在函数内部设置img = new value?

1. How can I get the value of img when I'm inside the function?
2. How can I sett img = new value from inside the function?

更新

此代码未给变量赋予新值:

This code does NOT give a new value to the variable:

    logoUrl = "noLogo.png";

    jQuery.post("my/path/somefile.php", { instance: 'getUrl', ownerID : "123", type: "brand"},
    function(logo)
    {
        logoUrl = logo.url + "logo/";
    },"json");      

    alert(logoUrl); // This outputs noLogo.png"

推荐答案

更新

在使用回调函数时，重要的是要注意执行流程:

When working with callback functions, its important to pay attention to execution flow:

var img = "nice.jpg";

$.post('/path', { key: value }, function(data){
   img = "newname.jpg";
});

alert(img); // Alerts "nice.jpg"

这是因为在回调(而不是在回调函数中)之后发生的所有代码都将首先执行:

It is because any code occurring after the callback (but not in the callback function) is executed first:

1. 将img设置为nice.jpg
2. 致电$.post
3. 致电alert
4. 将img设置为newname.jpg

1. Set img to nice.jpg
2. Call $.post
3. Call alert
4. Set img to newname.jpg

原始答案:

如果您使用的代码与您发布的代码完全相同，则:

If the code you are using exists exactly as you posted it, then:

1. img在匿名回调函数中已经可用.
2. 是的，您也可以在函数内部更改img的值.

1. img is already available inside your anonymous callback function.
2. Yes, you can change the value of img from inside the function as well.

使用var关键字声明变量时，该变量是其当前范围的私有变量，但可用于其范围内的任何其他上下文:

When you declare variable with the var keyword, it is private to its current scope, but is available to any other contexts contained within its scope:

作品

function getPost(){
   var img = "nice.jpg";

   $.post('/path', {key:value}, function(data){
       alert(img); // alerts "nice.jpg"
   });
}

不起作用

function changeImage(){
   var img = "nice.jpg";
   getPost();
}

function getPost(){
   $.post('/path', {key:value}, function(data){
       alert(img); // img is undefined
   });
}   

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