在函數內部實現回調函數

Question

說我有一個像下面這樣的函數。

loadXML('Method', requestString, function(callback){ 
    // The function as a callback parameter to loadXML goes here. 

    // Here I am calling the callback function like this  
    if(callback != null){ 
     callback(); 
    } 
}); 

但我想在loadXML函數裏面定義這個回調函數。那麼我可以像下面這樣做嗎？

loadXML('Method', requestString, function(callback){ 
    // The function as a callback parameter to loadXML goes here. 

    // Here I have to call the callback function like this, (do I?) which is a 
    // callback parameter to callback function of loadXML 
    callback = function(){ 
     // The callback function implementation goes here 
    } 
}); 

Answer 1

也許這可以幫助你瞭解嵌套回調機制：

var loadXML; 
var outerCB; 
var innerCB;  

loadXML = function(method, requestString, cb) { 
    // pass the innerCB implementation as argument to the outer cb 
    if('undefined' !== typeof innerCB) { 
    cb(innerCB); 
    } else { 
    // in case innerCB would not be defined 
    cb(function() { 
     console.log('hi from anonymous cb') 
    }); 
    } 
}; 


innerCB = function() { 
    console.log('hi from innerCB cb!') 
}; 

outerCB = function(callback) { 
    if('undefined' !== typeof callback) { 
    callback(); // innerCB();  
    } else { 
    console.log('no cb passed, do something else') 
    }  
} 

loadXML('Method', 'abcd', outerCB) // hi from innerCB cb!