Question

请考虑以下代码段：

$('#selectone').change(function(){
    var amount;
    $.get('search.php', {search:'units'}, function(result){
        //this will return only one or zero for me.
        amount = result;
    })
    if(amount>0)
    {
        alert('This option has been selected, please select another one');
    }
})

我的变量amount总是来undefined。如何修复或重构？

Answer 1

这是因为以下代码在$.get()请求中的回调函数之前运行：

if(amount>0)
{
    alert('This option has been selected, please select another one');
}

AJAX调用是异步的，这意味着它们周围的代码在AJAX调用等待响应时运行。因此，在AJAX回调触发之前if(amount>0)代码正在运行（这意味着if/then语句amount始终等于null。）

要做你想做的事情我建议把这些代码放在你的$.get()请求的回调函数中：

$('#selectone').change(function(){
    $.get('search.php', {search:'units'}, function(result){
        //this will return only one or zero for me.
        if(result>0)
        {
            alert('This option has been selected, please select another one');
        }
    });
});

<强> - 更新 -

您还可以使用jQuery的$.when()方法：

$('#selectone').change(function(){
    var amount;
    var jqXHR = $.get('search.php', {search:'units'}, function(result){
        //this will return only one or zero for me.
        amount = result;
    });
    $.when(jqXHR).then(function () {
        if(amount>0)
        {
            alert('This option has been selected, please select another one');
        }
    });
});

Answer 2

你不能只在成功函数中使用它吗？这将是最好的方式：

$('#selectone').change(function(){
 var amount;
    $.post({
        async : false, // this makes it possible
        url: 'search.php', 
        data: {search:'units'}, 
        success : function(result){
            //this will return only one or zero for me.
            amount = result;
        }
    });

    if(amount>0)
    {
        alert('This option has been selected, please select another one');
    }
})

我需要在jQuery中使用get函数之外的var

2 个答案: