Javascript匿名函数不更新全局变量 [英] Javascript anonymous function not updating global variable

问题描述

我在一些代码中看到了一个$ .getJSON调用，它似乎没有更新全局变量，我不知道为什么。 JSON数据正在加载OK，但出于某种原因，全局EventOptions数组未在for {}循环中更新。大写的注释是指变量。有任何想法吗？谢谢

 函数LoadMeasurementTypes（）{
 //清除EventOptions 
 EventOptions = [... ]; 
 //将一对夫妇推到EventOptions  - 这些添加成功
 EventOptions.push（Temperature）; 
 EventOptions.push（脉率）; 
 //调用json从表中获取measurementTypes 
 $ .getJSON（'./ get-measurement-types.php'，function（measurementTypeData）{
 //处理每个json元素（var i = 0; i< measurementTypeData.length; ++ i）{
 // e是存储变量[0] .BP，[1] .ph包含当前元素
 var e = measurementTypeData [i]; 
 //添加新的度量类型
 alert（e.measure_type）; // OK works  - 我们可以看到measure_type 
 EventOptions.push（e.measure_type）; //这些不会被添加
} 
} //结束匿名函数
）//结束获取json调用
 EventOptions .push（Last one）; //这是一个被添加
} 
  

解决方案您的 EventOptions [] 不是全局可见的。我的猜测是它应该仍然可以在您的$ .getJSON调用本地可见;但是因为它现在被限制在jquery中，所以它显然被掩盖了（你是否在你的匿名函数内测试了 alert（EventOptions）; ？）。

为了正确使用范围，只需在 LoadMeasureTypes（）之外声明它。

  var EventOptions = [...]; 
函数LoadMeasureTypes（）{... 
  

- 更新

如果这不起作用 - 您可以将匿名函数拉到$ .getJSON（）之外并为其指定一个变量名称：

  var retreiveTypes = function（）{...}; 
 
 $ .getJSON（.. path / php，retreiveTypes）; 
  

I've got a $.getJSON call in some code that appear to be not updating a global variable, and I'm at a loss to understand why. The JSON data is being loaded OK, but for some reason the global EventOptions array is not being updated in the for {} loop. The capitalised comments refer to the variable. Any ideas? Thanks

function LoadMeasurementTypes() {
    // Clear out EventOptions
    EventOptions = ["..."];
    // Push a couple on to EventOptions - THESE ADD OK
    EventOptions.push("Temperature");
    EventOptions.push("Pulse rate");
    // Call json to get measurementTypes off the table    
    $.getJSON('./get-measurement-types.php', function (measurementTypeData) {
        // Process each json element ([0].BP, [1].ph (Urine) etc.
        for (var i = 0; i < measurementTypeData.length; ++i) {
            // e is a storage variable to contain the current element
            var e = measurementTypeData[i];
            // Add the new measurement type
            alert(e.measure_type); // OK works - we can see the measure_type
            EventOptions.push(e.measure_type); // THESE ARE NOT BEING ADDED 
        }
    } // end anonymous function
    ) // end get json call
    EventOptions.push("Last one"); // THIS ONE IS BEING ADDED
}

解决方案

Your EventOptions[] is not globally visible. My guess would of been that it should still be visible locally to your $.getJSON call; but because it is now scoped to jquery, its clearly obscured (did you alert(EventOptions); inside your anon function to test?.

To properly scope, just declare it outside of LoadMeasureTypes().

var EventOptions = ["..."];
function LoadMeasureTypes(){...

-update

if this does not work - you could always pull the anonymous function outside of the $.getJSON() and assign it a variable name:

var retreiveTypes = function(){...};

$.getJSON("..path/php", retreiveTypes);

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