Java Reference
In-Depth Information
The first four statements of this function create four variables. The first, lstCity , contains a reference
to the <select/> element object. You create this variable for convenience purposes—namely for the
creation of the second variable: selectedOption :
var selectedOption = lstCity.options[lstCity.selectedIndex];
This selectedOption variable is retrieved by using the lstCity object's options property in
conjunction with its selectedIndex property, and now that you have the selectedOption , you can
easily get the information attached to the option:
var offset = selectedOption.value;
var selectedCity = selectedOption.text;
Next, you want to determine if the user checked the daylight savings check box:
var dstAdjust = 0;
if (myForm.chkDst.checked) {
dstAdjust = 60;
}
You initialize the dstAdjust variable with 0 . If the check box is checked, you modify dstAdjust to
contain the value of 60 . The value of 60 is for 60 minutes. As you have probably guessed, your time
conversion calculation will be with minute values.
In the final part of updateTimeZone() , you call the updateTime() function, passing the values
contained within the selectedCity , offset , and dstAdjust variables:
updateTime(selectedCity, offset, dstAdjust);
}
In the function updateTime() , you write the current local time and the equivalent time in the selected
city to the output elements.
You start at the top of the function by creating a new Date object, which is stored in the variable
now . The Date object will be initialized to the current local time:
function updateOutput(selectedCity, offset, dstAdjust) {
var now = new Date();
Next, you output the local time to the <span/> element with an id of spanLocalTime :
document.getElementById("spanLocalTime").innerHTML = now.toLocaleString();
You use the Date object's toLocaleString() method to format the date and time in your region's
format.
You saw in Chapter 7 that if you set the value of a Date object's individual parts (such as hours,
minutes, and seconds) to a value beyond their normal range, JavaScript assumes you want to adjust the
date, hours, or minutes to take this into account. For example, if you set the hours to 36 , JavaScript
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