Javascript：为什么不能在回调函数中获取变量？答案

【问题标题】：Javascript: Why can not get variable in callback function?Javascript：为什么不能在回调函数中获取变量？
【发布时间】：2018-10-18 06:40:33
【问题描述】：

我已经阅读了几个不同的callback 函数文档，但不幸的是无法成功获得相关的variable。我在这里缺少什么？

checkNo: function (callback) {
    var comboQuery = Ext.ComponentQuery.query('[name=foocombo]')[0].getSelectedRecord();
    var chkno = comboQuery.get('mychkno'); //Success to get this integer value

    callback(chkno); //Error raises here. Debugger says "callback is not a function"
    //if (callback) callback(chkno); //I've tried to check callback but did not work as well.
},

setFooCombo: function () {
    var me = this;
    var fooStore = Ext.getStore('fooComboStore');
    var chkno = ''; //Trying to pass an empty value. Not sure if correct approach 
    var checkno = me.checkNo(chkno); //Trying to get returned value from above function to be able using on url.

    fooStore.getProxy().setUrl(MyApp.Url() + '/foo/list?=' + checkno); //I need pass value that return from callback to here
    if (typeof checkno === MyApp.NUMBER) {
        fooStore.load();
    }


    // I've tried another way to set new URL as below but did not work too.
    // me.checkNo(function (checkno) {
    //fooStore.getProxy().setUrl(MyApp.Url() + '/foo/list?=' + checkno);
    //     if (typeof checkno === MyApp.NUMBER) {
    //         fooStore.load();
    //     }
    // });
},

更新：在 Rahul Khandelwal 的回答重构了函数之后，当然现在可以工作了。

checkNo: function () {
    var comboQuery = Ext.ComponentQuery.query('[name=foocombo]')[0].getSelectedRecord();
    var chkno = comboQuery.get('checkno');

    return chkno;

},

setFooCombo: function () {
    var me = this;
    var fooStore = Ext.getStore('fooComboStore');
    var checkno = me.checkNo();

    fooStore.getProxy().setUrl(MyApp.Url() + '/foo/list?=' + checkno);
    if (typeof checkno === MyApp.NUMBER) {
        fooStore.load();
    }
},

【问题讨论】：

你没有传递函数。
另外，chkno 定义在 setFooCombo 而不是 checkNo - 它不是函数，因此 callback 不是函数'
因为 checkNo 似乎充满了 syncrhonous 代码，反正你不需要回调

标签： javascript function extjs callback

【解决方案1】：

在调用函数时，您没有使用回调功能。将其更改为正常的函数定义，如下所示。

CheckNo: function () {
var comboQuery = Ext.ComponentQuery.query('[name=foocombo]')[0].getSelectedRecord();
var chkno = comboQuery.get('mychkno'); //Success to get this integer value

return chkno; //Error raises here. Debugger says "callback is not a function"
//if (callback) callback(chkno); //I've tried to check callback but did not work as well.

}

要了解回调的工作原理，请使用以下链接：

This StackOverflow question

【讨论】：

【解决方案2】：

me.checkNo(function(){ return checkNo;})

【讨论】：