And knowing how to work with the
Date() object would be your job in such cases.
The Date() constructor
When used without any arguments at all the function returns the current date:
var date = new Date(); console.log(date);
Setting the date
Apart from getting the current date, we can also use the
Date() constructor to set the date manually.
When given a single argument, the argument is treated as the number of milliseconds since Jan 01 1970.
Consider the example below where we set the date to 1 second above the starting time.
var date = new Date(1000); // 1000ms above Jan 1970.
Not only this but the
Date() constructor can also take multiple arguments in the order year, month, day, hours, minutes and seconds.
new Date(year, month, day, hours, minutes, seconds)
Let's demonstrate a few examples:
Year 2000, and month January:
var date = new Date(2000, 0); console.log(date);
Year 2000, month January and day 3:
var date = new Date(2000, 0, 3);
Year 2000, month January, day 3 and 6th hour:
var date = new Date(2000, 0, 3, 6);
06:00:00here - it indeed indicates the 6th hour.
And the rest you should try out yourself!
In the examples above we specified the month, day, hour in normal ranges. However we can also go beyond them in which case the function will resolve the overhead itself.
For instance in the following example we set the the date to 24 months after 2000 01 Jan:
var date = new Date(2000, 24);
We can also use negative values to go backwards:
var date = new Date(2000, -12);
The same also applies to day, hours etc.
Following we set the date to 367 days since 31 Dec 2000.
var date = new Date(2000, 0, 367);
Date setter methods
In all the examples above we utilised the
Date() constructor directly to set given dates, but now we will take a look at some of its methods to do this job.
setMilliseconds() set the corresponding part of the given date to the given value.
var date = new Date(); // current date date.setYear(90); // the year becomes 1990
setYear()sets ONLY the year of the current date to the given value - the rest remains the same i.e the seconds, minutes, hours still increment!
One thing to note about all these methods is that they return a number in milliseconds since
new Date(0) corresponding to the value you gave to them. This means that to show the new date we first have to convert this milliseconds format into a more readable one.
And we can do that using either the
Date() constructor directly or some methods on it to convert between formats.
Going with the former choice we have the following:
var date = new Date(); date.setYear(90); date = new Date(date); // milliseconds given to Date()
Another method similar to
setFullYear() which won't round values in the range 0-99 to 1990-1999 respectively.
var date = new Date(); // current date date.setFullYear(90); // the year becomes 0090
The concepts discussed above for the other parts like month, days also apply to these setting methods. For example
setMonth(-24) will go 24 months backwards from the given date.
Date getter methods
Similar to the setter methods we also have date getter methods with essentially the same end-naming.
getMilliseconds() get the corresponding part of the given date.
Following we get the year of the current date using
getFullYear(). We use it instead of
getYear() to get the full year and not any shortened form which we will otherwise have to process further:
var date = new Date(); // current date date.getYear();
var date = new Date(2000, 0); // 200, Jan 01 date.getYear();
The last concept left to be covered in this chapter is how to display dates in a readable format.
To display the whole date including the time in UTC Format we can use the method
toUTCString(). To match locale of the operating system we can use
var date = new Date(); // current date date.toUTCString(); date.toLocaleString();
To display the date only in a more humanly readable format we can use the method
toDateString() and for matching the locale of the OS we can use
var date = new Date(); // current date date.toDateString(); date.toLocaleDateString();
To display the time only we can use the method
toTimeString() and for matching the locale of the OS we can use
var date = new Date(); // current date date.toTimeString(); date.toLocaleTimeString();
When you feel you are all perfect with them move on to the next avenue in this course - Dates quiz.