为什么javascript无法修改我的变量？

Question

我使用以下javascript函数遇到的问题是，它以“不是程序员”的身份返回最流行的字符串值，因此尽管它在执行我的console.log命令的位置时执行了正确的操作，但返回的最流行的变量hasn没有被修改。 如果我在顶部修改变量，为什么它不返回修改...就像javascript生成一个实例一样，它仅在测试函数的本地设置中起作用（如果我将console.log语句打印出来，正确的数据）。 为什么是这样 ？

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

如上所述，历史记录搜索是异步的，因此完成后需要回调执行

它将像下面这样工作：

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;