爲什麼JavaScript不能修改我的變量？

Question

我在使用下面的javascript函數時遇到的問題是，它將大多數流行的字符串值作爲「不是程序員」返回，因此儘管它正在執行正確的操作，而我的console.log命令被放置，它將返回最流行的變量沒有被修改。如果我正在修改頂部的變量，爲什麼不返回修改......它幾乎就像JavaScript創建一個實例，它只能在測試函數的本地設置中工作（如果我將它放在console.log語句中，它會打印出來正確的數據）。爲什麼是這樣 ？

var mostPopular = "not a programmer"; 
var totalResults = 0; 


function myfunction() { 
    var listOfLanguages = ["Java", "C", "C++", "PHP", "C#", "Visual Basic", "Python", "Objective-C", "Perl", "Javascript", "Ruby"]; 



    for (var i = 0; i < listOfLanguages.length - 1; i++) { 
     chrome.history.search({ 
      text: listOfLanguages[i], 
      maxResults: 100 
     }, function (search_results) { 

      var countOfResults = search_results.length; 
      var langOfResults = listOfLanguages[i - 1]; 

      test(countOfResults, langOfResults); 

     }); 

    } 

    console.log(mostPopular); 
} 

function test(count, lang) { 


    if (count > totalResults) { 

     totalResults = count; 
     mostPopular = lang; 
    } 

} 

window.onload = myfunction; 

Answer 1

由於歷史搜索上面提到的是異步的，因此完成

時，會像下面這需要一個回調執行：

var mostPopular = "not a programmer"; 
var totalResults = 0; 


function myfunction() { 
    var listOfLanguages = ["Java", "C", "C++", "PHP", "C#", "Visual Basic", "Python", "Objective-C", "Perl", "Javascript", "Ruby"]; 



    for (var i = 0; i < listOfLanguages.length - 1; i++) { 
     chrome.history.search({ 
      text: listOfLanguages[i], 
      maxResults: 100 
     }, function (search_results) { 

      var countOfResults = search_results.length; 
      var langOfResults = listOfLanguages[i - 1]; 

      test(countOfResults, langOfResults); 
      console.log(mostPopular); 
      // The Code will execute whenever the history search results are returned 
     }); 

    } 
// Any code here will be exceuted irrespective of the history search completed or not 

} 

function test(count, lang) { 


    if (count > totalResults) { 

     totalResults = count; 
     mostPopular = lang; 
    } 

} 

window.onload = myfunction;