Question

我有两个字符串变量：month1Digit1和month1Digit2。它们一起组成一个月的十进制数字（01-12），因此month1Digit1总是0或1，而month1Digit2可以是0以外的任何数字。现在我有几个，如month2Digit1，等等。想要一个可以从这些变量中确定月份名称的函数。但我不想为每个组编写一个单独的函数，因为它有不同的变量。从搜索周围看起来我需要用参数做一个函数，但我不确定这是如何工作的。我尝试了以下方法：

var month1Digit1 = "1";
var month1Digit2 = "2";

function getMonthName (month) {
    if (month == "1") { month = "January" }
    else if (month == "2") { month = "February" }
    else if (month == "3") { month = "March" }
    else if (month == "4") { month = "April" }
    else if (month == "5") { month = "May" }
    else if (month == "6") { month = "June" }
    else if (month == "7") { month = "July" }
    else if (month == "8") { month = "August" }
    else if (month == "9") { month = "September" }
    else if (month == "10") { month = "October" }
    else if (month == "11") { month = "November" }
    else if (month == "12") { month = "December" }
}

var orangemonth1 = month1Digit1 + month1Digit2;
getMonthName(orangemonth1);
orangedate = orangemonth1;

现在，橙色日期的值应该是'十二月'，不是吗？但是当我运行它时，我得到“12”作为值。所以功能不起作用。我做错了什么？

Answer 1

你抓到了一只红鲱鱼。

function foo(in) {
    in = 2;
}
var a = 1;
foo(a);
console.log(a); // prints 1

你的问题远不及字符串连接或与字符串连接有关;你理解得当。您需要了解Javascript是通过引用副本传递的，并且您正在更改引用的副本。见这里：Is JavaScript a pass-by-reference or pass-by-value language?

Answer 2

我会使用数组将月份映射到您使用的编号系统，并从函数返回结果：

var month1Digit1 = '0';
var month1Digit2 = '7';

var monthMap = ['', 'January', 'February', 'March', 'April', 'May', 'June', 'July', 'August', 'September', 'October', 'November', 'December'];

function getMonthName (input) {
    var monthNumber = parseInt(input);
    return monthMap[monthNumber];
}

var orangemonth1 = month1Digit1 + month1Digit2;
orangedate = getMonthName(orangemonth1);

alert(orangedate);

Demo on JSFiddle

Answer 3

问题是你没有返回任何变量而没有分配它值仅更改为您案例中的函数试试这个：

var month1Digit1 = "1";
var month1Digit2 = "2";

function getMonthName (month) {
    if (month == "1") { month = "January" }
    else if (month == "2") { month = "February" }
    else if (month == "3") { month = "March" }
    else if (month == "4") { month = "April" }
    else if (month == "5") { month = "May" }
    else if (month == "6") { month = "June" }
    else if (month == "7") { month = "July" }
    else if (month == "8") { month = "August" }
    else if (month == "9") { month = "September" }
    else if (month == "10") { month = "October" }
    else if (month == "11") { month = "November" }
    else if (month == "12") { month = "December" }

    return (month);
}

var orangemonth1 = month1Digit1 + month1Digit2;
orangedate = getMonthName(orangemonth1);

Answer 4

你没有从你的功能中返回任何东西。

function getMonthName (month) {
    if (month == "1") { month = "January" }
    else if (month == "2") { month = "February" }
    else if (month == "3") { month = "March" }
    else if (month == "4") { month = "April" }
    else if (month == "5") { month = "May" }
    else if (month == "6") { month = "June" }
    else if (month == "7") { month = "July" }
    else if (month == "8") { month = "August" }
    else if (month == "9") { month = "September" }
    else if (month == "10") { month = "October" }
    else if (month == "11") { month = "November" }
    else if (month == "12") { month = "December" }
    return month;
}

Answer 5

变量month按值传递 - 也就是说，当您调用getMonthName时，month是COPY的orangemonth1，而不是变量本身。因此，当你改变月份时，你不会影响橘子。

尝试将return month添加到getMonthName

的末尾

Answer 6

你可以试试这个;

function getMonthName(month) {
    var months = ["", "January", "February", "March", "April", "May", "June", 
                  "July", "August", "September", "October", "November", "December"];
    // or
    var months = {1:"January", 2:"February", 3:"March", 4:"April", 5:"May", 6:"June", 
                  7:"July", 8:"August", 9:"September", 10:"October", 11:"November", 12:"December"};

    return months[parseInt(month)];
}

console.log(getMonthName(1));

Answer 7

我认为你错过了变量是通过引用还是通过值传递到javascript中的函数的问题。答案并不像人们想象的那么简单。看看这个问题。

Is JavaScript a pass-by-reference or pass-by-value language?

无论如何，如果你想让这个工作，而不是假设你的变量已在函数内被改变，显式返回你的新值，而不是month

function getMonthName (month) { if (month == "1") { month = "January" }... etc etc return month; }

此后，您需要像这样调用您的函数：

var textMonth = getMonthName(orangemonth1);

带参数的Javascript函数

7 个答案: