简单的 JavaScript 没有执行？

Question

validateDate() 函数在调用时不执行的原因可能是什么？

validateDate() 的目的是取01/01/2001 之类的字符串并调用isValidDate() 来判断日期是否有效。

如果无效，则会出现警告消息。

 function isValidDate(month, day, year){
    /*
    Purpose: return true if the date is valid, false otherwise

    Arguments: day integer representing day of month
    month integer representing month of year
    year integer representing year

    Variables: dteDate - date object

    */
    var dteDate;

    //set up a Date object based on the day, month and year arguments
    //javascript months start at 0 (0-11 instead of 1-12)
    dteDate = new Date(year, month, day);

    /*
    Javascript Dates are a little too forgiving and will change the date to a reasonable guess if it's invalid. We'll use this to our 
    advantage by creating the date object and then comparing it to the details we put it. If the Date object is different, then it must
    have been an invalid date to start with...
    */

    return ((day == dteDate.getDate()) && (month == dteDate.getMonth()) && (year == dteDate.getFullYear()));
 }

 function validateDate(datestring){

     month = substr(datestring, 0, 2);
     day   = substr(datestring, 2, 2);
     year  = substr(datestring, 6, 4);

     if(isValidDate(month, day, year) == false){
         alert("Sorry, " + datestring + " is not a valid date.\nPlease correct this.");
         return false;
     } else {
         return true;
     }
 }

Answer 1

substr 本身不是一个函数；你必须使用string.substr(start_index, length)。

由于JavaScript substr method 只接受两个参数，而不是三个参数，这会导致执行在第一个 substr 行停止，并且您将永远无法从该函数获得输出。

我在测试 HTML 页面中运行代码时打开 Firebug 发现了这一点。我强烈推荐使用Firebug 进行 JavaScript 调试。

在你的 validateDate 函数中试试这个，或者类似的东西：

month = datestring.substr(0, 2);
day   = datestring.substr(3, 2);
year  = datestring.substr(6, 4);

Answer 2

substr 没有定义...你需要

datestring.substr(0, 2);

您的第二个子字符串也有问题 - 它应该从字符 3 开始：

day   = substr(datestring, 3, 2);

而且，当您创建日期时，月份确实应该是 (month - 1)

Answer 3

查看您的代码，您的日期格式是“MMDD__YYYY”。所以你的函数需要如下：

 function isValidDate(month, day, year){
    /*
    Purpose: return true if the date is valid, false otherwise

    Arguments: day integer representing day of month
    month integer representing month of year
    year integer representing year

    Variables: dteDate - date object

    */
    var dteDate;

    //set up a Date object based on the day, month and year arguments
    //javascript months start at 0 (0-11 instead of 1-12)
    dteDate = new Date(year, month, day);
    alert(d)

    /*
    Javascript Dates are a little too forgiving and will change the date to a reasonable guess if it's invalid. We'll use this to our 
    advantage by creating the date object and then comparing it to the details we put it. If the Date object is different, then it must
    have been an invalid date to start with...
    */

    return ((day == dteDate.getDate()) && (month == dteDate.getMonth()) && (year == dteDate.getFullYear()));
 }

 function validateDate(datestring){

     month = datestring.substring(0, 2);
     day   = datestring.substring(2, 4);
     year  = datestring.substring(6, 10);
     alert(year)

     if(isValidDate(month, day, year) == false){
         alert("Sorry, " + datestring + " is not a valid date.\nPlease correct this.");
         return false;
     } else {
         return true;
     }
 }
validateDate("0202__2010");

如果您的日期格式更常规，您可以执行以下操作来测试if ((new Date("MM/DD/YYYY")) != "Invalid Date")