可以通过两种方式使用JavaScript代码。
- 可以在HTML文档本身内部包含JavaScript代码
- 可以将JavaScript代码保存在单独的外部文件中，然后从HTML文档指向该文件。
什么是内部JavaScript
到目前为止，我们一直在使用内部JS。这是一个样本-
<html>
<head>
<title>
My First JavaScript code!!!
</title>
<script type="text/javascript">
// Create a Date Object
var day = new Date();
// Use getDay function to obtain todays Day.
// getDay() method returns the day of the week as a number like 0 for Sunday, 1 for Monday,….., 5
// This value is stored in today variable
var today = day.getDay();
// To get the name of the day as Sunday, Monday or Saturday, we have created an array named weekday and stored the values
var weekday = new Array(7);
weekday[0]="Sunday";
weekday[1]="Monday";
weekday[2]="Tuesday";
weekday[3]="Wednesday";
weekday[4]="Thursday";
weekday[5]="Friday";
weekday[6]="Saturday";
// weekday[today] will return the day of the week as we want
document.write("Today is " + weekday[today] + ".");
</script>
</head>
<body>
</body>
</html>什么是外部JavaScript？
计划在所有网页中显示当前日期和时间。假设这将是一项非常耗时且困难的任务。
因此，将JavaScript代码保存在扩展名为.js的新文件中。然后，在所有网页中添加一行代码，以指向.js文件，如下所示：
注意：假设.js文件和所有网页都在同一文件夹中。如果外部.js文件位于不同的文件夹中，则需要在src属性中指定文件的完整路径。
如何链接外部JavaScript
var currentDate = new Date();
var day = currentDate.getDate();
var month = currentDate.getMonth() + 1;
var monthName;
var hours = currentDate.getHours();
var mins = currentDate.getMinutes();
var secs = currentDate.getSeconds();
var strToAppend;
if (hours >12 )
{
hours1 = "0" + (hours - 12);
strToAppend = "PM";
}
else if (hours <12)
{
hours1 = "0" + hours;
strToAppend = "AM";
}
else
{
hours1 = hours;
strToAppend = "PM";
}
if(mins < 10)
mins = "0" + mins;
if (secs<10)
secs = "0" + secs;
switch (month)
{
case 1:
monthName = "January";
break;
case 2:
monthName = "February";
break;
case 3:
monthName = "March";
break;
case 4:
monthName = "April";
break;
case 5:
monthName = "May";
break;
case 6:
monthName = "June";
break;
case 7:
monthName = "July";
break;
case 8:
monthName = "August";
break;
case 9:
monthName = "September";
break;
case 10:
monthName = "October";
break;
case 11:
monthName = "November";
break;
case 12:
monthName = "December";
break;
}
var year = currentDate.getFullYear();
var myString;
myString = "Today is " + day + " - " + monthName + " - " + year + "Current time is " + hours1 + ":" + mins + ":" + secs + " " + strToAppend + ".";
document.write(myString);这是currentDetails.js文件。务必对HTML文档进行如下更改：
<html>
<head>
<title>
My External JavaScript Code!!!
</title>
<script src="currentdetails.js" type="text/javascript">
</script>
</head>
<body>
</body>
</html>何时使用内部和外部JavaScript代码
如果只有几行特定于特定网页的代码，那么最好将JavaScript代码保留在HTML文档内部。 另一方面，如果JavaScript代码在许多网页中使用，那么应该考虑将代码保存在一个单独的文件中。有助于轻松调试。
