At times, it becomes necessary to determine the week number of the current week or to find the week number corresponding to a specific date. This challenge can be addressed using the JavaScript programming language. JavaScript provides various date-related functions, including getDays, getMonth, and getTime, which can be utilized for handling date operations. Additionally, mathematical functions like Math.floor and Math.ceil assist in computing the week number effectively.
Situation
In this method, we will allocate a specific number to every day of the week, for instance, designating 1 for Sunday, 2 for Monday, 3 for Tuesday, and continuing in this manner. Likewise, each of the remaining days will receive a corresponding number. It is important to remember that the week begins with Sunday and concludes with Saturday.
Assuming today is Monday and we are currently in week number 1, if we determine the week number after a span of 25 days, it will fall in the 4th week.
According to the week number calculation:
25 days = 7 + 7 + 7 + 4 days
The formula outlined below is utilized to determine the week number after a period of p days:
Week Number = least integer [ p / 7 ]
We can apply this idea in our JavaScript example to determine the week number. The calculation of the week number will be performed in two different methods:
- Determine the week number for the present date
- Determine the week number for a specified date
We will explore both techniques thoroughly with illustrative examples. Additionally, we will dynamically compute the weekdays by receiving date inputs from users through an interactive HTML form.
- Determine the week number by capturing date inputs via a dynamic HTML form.
Approach 1: Calculate Week Number of current date
In this approach, we will find the week number of current date means the date will be taken from the system. It is a static way to calculate the week number. Follow each step for calculating weekdays:
- Define a date variable todaydate and oneJan in JavaScript.
- Initialize the todaydate variable by creating the date object using new Date , which will take system date by default.
- Initialize another variable oneJan by creating date object using new Date but this time getFullYear method inside it.
- The getFullYear function will return the year of current date along with first date of the year, e.g., 1 Jan 2020.
- After getting the current date and year, now calculate the number of days using the Math.floor method. So, calculate the difference of current date and current year date and divide it by total milliseconds in a day (10006060*24).
- Now, add 1 and numberofdays calculated in previous result to the day of current date and divide them by 7, i.e., (this.getDay + 1 + numberofdays) / 7. Don't forget to put this whole calculation of step 6 inside Math.ceil method.
- Finally, display the calculated weekday on the web using document.write .
At this point, we will translate these steps into concrete implementation. Below is the corresponding code:
Copy Code
<html>
<head>
<title>Calculate week number of current date</title>
</head>
<body>
<script>
//define a date object variable that will take the current system date
todaydate = new Date();
//find the year of the current date
var oneJan = new Date(todaydate.getFullYear(), 0, 1);
// calculating number of days in given year before a given date
var numberOfDays = Math.floor((todaydate - oneJan) / (24 * 60 * 60 * 1000));
// adding 1 since to current date and returns value starting from 0
var result = Math.ceil(( todaydate.getDay() + 1 + numberOfDays) / 7);
//display the calculated result
document.write("Week Numbers of current date (" + todaydate +
") is: <br>" + result);
</script>
</body>
</html>
Output
Week number of current date (Tue Sep 29 2020 15:32:19 GMT+0530 (India Standard Time)) is:
40
Screenshot
Approach 2: Calculate the week number for a predefined date
This approach will help to calculate the week number by providing a date in code. Follow the below step:
- Define a date variable in JavaScript, i.e., date1
- Initialize it by creating the date objects using new Date and provide date inside it.
- After defining the date, calculate the time difference between them by subtracting one date from another date using date2.getTime - date1.getTime;
- Now next step is to calculate the days between the dates. So, we will divide the time difference of both dates by the milliseconds in a day, i.e., 10006060*24
- At last, print the result calculated using the document.write method.
At this point, we will translate the aforementioned steps into a practical application. Please refer to the code provided below:
Copy Code
<html>
<head>
<title>Calculate week number of predefined date</title>
</head>
<body>
<script>
//define a date object variable with date inside it
var date1 = new Date("11/27/2019");
//find the year of the entered date
var oneJan = new Date(date1.getFullYear(), 0, 1);
// calculating number of days in given year before the given date
var numberOfDays = Math.floor((date1 - oneJan) / (24 * 60 * 60 * 1000));
// adding 1 since to current date and returns value starting from 0
var result = Math.ceil(( date1.getDay() + 1 + numberOfDays) / 7);
//display the calculated result
document.write("Week Numbers of date (" + date1 +
") is: <br>" + result);
</script>
</body>
</html>
Output
Week number of date Wed Nov 27 2019 00:00:00 GMT+0530 (India Standard Time):
48
Screenshot
Calculate Week Number by entering a date using HTML form
In this method, we will determine the week number by submitting a date through a dynamic HTML form. The user has the option to select a date from a calendar and input it into a designated field within the HTML form. This provides a dynamic approach for calculating the week number, enabling users to input their own dates directly on the web rather than having the programmer hard-code the date inputs.
See the code below:
Copy Code
<html>
<head>
<title> Calculate week number by user input </title>
<script>
function weekNumber() {
//define a variable and fetch the input from HTML form
var dateinput = document.getElementById("dateInput1").value;
//create a date object variable to store the date values
var date1 = new Date(dateinput);
//find the year of the current date
var oneJan = new Date(date1.getFullYear(), 0, 1);
// calculating number of days in given year before the given date
var numberOfDays = Math.floor((date1 - oneJan) / (24 * 60 * 60 * 1000));
// adding 1 since to current date and returns value starting from 0
var result = Math.ceil(( date1.getDay() + 1 + numberOfDays) / 7);
//return the calculated result and display it
return document.getElementById("result").innerHTML = "Week number of given date is: " + result;
}
</script>
</head>
<body>
<h2 style="color: 32A80F" align="Center">
Result: Calculate Week Number using user input
<br> <br> </h2>
<p align="Center"> <b> Enter date </b>
<input type="date" id="dateInput1">
<br> <br>
<button onclick="weekNumber()">
Calculate Week Number
</button>
</p>
<h3 style="color:32A80F" id="result" align="center"></h3>
</body>
</html>
Screenshot
Examine the screenshot provided below, which showcases an HTML form that includes a calendar-type input field, a submit button designed to execute all necessary calculations, and an additional field intended for displaying the results of those calculations.