Using answers from prompt for a calculation - javascript

Total newbie at JavaScript.
I would like to calculate how many days one has been alive by asking the user their date of birth via prompts/alerts, then obviously subtracting their date of birth from today's date.
I've made a bit of a start...
var month=prompt("Please enter month of birth"," ");
var day=prompt("Please enter day of birth"," ");
var year=prompt("Please enter your year of birth"," ");
var curdate = this is the bit i need help with
var birth = this is the bit i need help with
var milliDay = 1000 * 60 * 60 * 24; // a day in milliseconds;
var ageInDays = (curdate - birth) / milliDay;
document.write("You have been alive for: " + ageInDays);
Any advice or help would be much appreciated.

You need to use the Date object (MDN). They can be created from a month, a day, and a year, and added/subtracted.
Typically :
var curDate = new Date();
var birth = new Date(year, month, day);
var ageInDays = (curdate.getTime() - birth.getTime()) / milliDay;
Be aware of the fact that months starts at 0, e.g. January is 0.

var curDate = new Date();
gives you the current date.
var birthdate = new Date(year, month-1, day);
gives you a Date from the separate variables. NB the month is zero-based.

end = Date.now(); // Get current time in milliseconds from 1 Jan 1970
var date = 20; //Date you got from the user
var month = 8-1; // Month, subtracted by one because month starts from 0 according to JS
var year = 1996; // Year
//Set date to the old time
obj = new Date();
obj.setDate(date);
obj.setMonth(month);
obj.setYear(year);
obj = obj.getTime(); //Get old time in milliseconds from Jan 1 1970
document.write((end-obj)/(1000*60*60*24));
Simply subtract current time from Jan 1 1970 in milliseconds from their birthdate's time from Jan 1 1970 in milliseconds. Then convert it to days. Look at MDN's Docs for more info.
See JSFiddle for a working example. Try entering yesterday's date. It should show 1 day.

Read some of this: http://www.w3schools.com/js/js_obj_date.asp

Related

Today's date -30 days in JavaScript

I need to get today's date -30 days but in the format of: "2016-06-08"
I have tried setDate(date.getDate() - 30); for -30 days.
I have tried date.toISOString().split('T')[0] for the format.
Both work, but somehow cannot be used together.
setDate() doesn't return a Date object, it returns the number of milliseconds since 1 January 1970 00:00:00 UTC. You need separate calls:
var date = new Date();
date.setDate(date.getDate() - 30);
var dateString = date.toISOString().split('T')[0]; // "2016-06-08"
You're saying that those two lines worked for you and your problem is combining them. Here is how you do that:
var date = new Date();
date.setDate(date.getDate() - 30);
document.getElementById("result").innerHTML = date.toISOString().split('T')[0];
<div id="result"></div>
If you really want to subtract exactly 30 days, then this code is fine, but if you want to subtract a month, then obviously this code doesn't work and it's better to use a library like moment.js as other have suggested than trying to implement it by yourself.
Please note that you would be better to use something like moment.js for this rather than reinventing the wheel. However a straight JS solution without libraries is something like:
var date = new Date();
date.setDate(date.getDate() - 30);
sets date to 30 days ago. (JS automatically accounts for leap years and rolling over months less than 30 days, and into the previous year)
now just output it like you want (gives you more control over the output). Note we are prepending a '0' so that numbers less than 10 are 0 prefixed
var dateString = date.getFullYear() + '-' + ("0" + (date.getMonth() + 1)).slice(-2) + '-' + ("0" + date.getDate()).slice(-2)
// Format date object into a YYYY-MM-DD string
const formatDate = (date) => (date.toISOString().split('T')[0]);
const currentDate = new Date();
// Values in milliseconds
const currentDateInMs = currentDate.valueOf();
const ThirtyDaysInMs = 1000 * 60 * 60 * 24 * 30;
const calculatedDate = new Date(currentDateInMs - ThirtyDaysInMs);
console.log(formatDate(currentDate));
console.log(formatDate(calculatedDate));
Today's date -30 days in this format: "YYYY-MM-DD":
var date = new Date();
date.setDate(date.getDate() - 30);
var dateString = date.toISOString().split('T')[0]; // "2021-02-05"
Today's date -30 days but get all days in this format: "YYYY-MM-DD":
var daysDate = [];
for(var i = 1; i<= 30; i++) {
var date = new Date();
date.setDate(date.getDate() - i);
daysDate.push(date.toISOString().split('T')[0]); // ["2021-02-05", "2021-02-04", ...]
}
Simply you can calculate in terms of timestamp
var date = new Date(); // Current date
console.log(date.toDateString())
var pre_date = new Date(date.getTime() - 30*24*60*60*1000);
// You will get the Date object 30 days earlier to current date.
console.log(pre_date.toDateString())
Here 30*24*60*60*1000 refers to time difference in miliseconds.

Increment JavasScript date object for next month when days are increased?

Is there a simple solution to auto increment the month of the date object when days are added via getDate?
I need to add 2 days to a user supplied date, for example if the user's entered value is 2014-11-16 it returns 2014-11-18.
I have this working in the below example, but the problem is if a user supplies a date at the end of the month, for example 2014-11-30 it will return 2014-11-32 (November only has 30 days) instead of rolling into the next month, it should be 2014-12-02.
It also does not increment to a new year as well.
var actualDate = new Date(arrive);
var year = actualDate.getFullYear();
var monthy = actualDate.getMonth()+1;
var days = actualDate.getDate()+2;
var out = year + '-' + (monthy < 10 ? '0' : '') + monthy + '-' + days;
http://jsfiddle.net/bubykx1t/
Just use the setDate() method.
var actualDate = new Date(arrive);
actualDate.setDate(actualDate.getDate() + 2);
Check out this link
You can create new Date objects based on the number of milliseconds since January 1, 1970, 00:00:00 UTC. Since the number of milliseconds in a minute, hour, day, week are set we can add a fixed amount to the current time in order to get a time in the future. We can forget about what day of the month, or year it is as it's inherent in the number of milliseconds that have passed since 1970.
This will keep adjust to days months and years correctly.
var numberOfDaysToIncrement = 7;
var offset = numberOfDaysToIncrement * 24 * 60 * 60 * 1000;
var date = new Date();
var dateIncremented = new Date(date.getTime() + offset);

Comparing two dates in JavaScript

I am currently trying to compare the launch_date with today's date. Let's say if the launch_date is within 3 years from today's date, it should perform something but I only managed to come out with some portion of the code:
var today = new Date();
var launch_date = 2011/10/17 00:00:00 UTC;
//if today's date minus launch_date is within 3 years, then do something.
Any guides? Thanks in advance.
To explicitly check for the three year range
var ld = new Date('2011/10/17 00:00:00 UTC')
if(today.getFullYear() - ld.getFullYear() < 3) {
//do something
}
This will fail on an invalid date string and possibly some other edge cases.
If you'll be doing a lot of date calculations I highly recommend Moment: http://momentjs.com/
you could always calculate the timespan in days and use that.
var getDays = function(startDate, endDate){
var ONE_DAY = 1000 * 60 * 60 * 24;
var difference = endDate.getTime() - startDate.getTime();
return Math.round(difference / ONE_DAY);
}
See this JsFiddle: http://jsfiddle.net/bj4Dq/1/
Try-
var today = new Date();
var launch_date = new Date("2011/10/17 00:00:00 UTC");
var diff = today.getYear() - launch_date.getYear();
if(diff <=3 )
alert("yes");
else
alert("no");
jsFiddle
you can create a Date object and invoke getTime() method (returns numer of milliseconds since 1970-01-01). Use one of this rows:
var yourDate = new Date(dateString) // format yyyy-mm-dd hh:mm:ss
var yourDate = new Date(year, month, day, hours, minutes, seconds, milliseconds)
After in the if statement use this condition:
var edgeDate = // new Date(dateString);
if ( (today.getTime () - yourDate.getTime ()) >= edgeDate.getTime() ){
// do something
}
Regards,
Kevin

Time between two times on current date

I am trying to calculate the time between two times on the current date using JavaScript. There are other questions similar to this one, but none seem to work, and few with many upvotes that I can find.
I have the following, which fails on the line: var diff = new Date(time1 - time2);, which always gives me an invalid Date when alerted, so it is clearly failing. I cannot work out why.
The initial date is added in the format of: hh:mm:ss in an input field. I am using jQuery.
$(function(){
$('#goTime').click(function(){
var currentDate = new Date();
var dateString = (strpad(currentDate.getDate()) +'-'+ strpad(currentDate.getMonth()+1)+'-'+currentDate.getFullYear()+' '+ $('#starttime').val());
var time1 = new Date(dateString).getTime();
var time2 = new Date().getTime();
var diff = new Date(time1 - time2);
var hours = diff.getHours();
var minutes = diff.getMinutes();
var seconds = diff.getMinutes();
alert(hours + ':' + minutes + ':' + seconds);
});
});
function strpad(val){
return (!isNaN(val) && val.toString().length==1)?"0"+val:val;
}
dateString is equal to: 14-01-2013 23:00
You have the fields in dateString backwards. Swap the year and day fields...
> new Date('14-01-2013 23:00')
Invalid Date
> new Date('2013-01-14 23:00')
Mon Jan 14 2013 23:00:00 GMT-0800 (PST)
dd-MM-yyyy HH:mm is not recognized as a valid time format by new Date(). You have a few options though:
Use slashes instead of dashes: dd/MM/yyyy HH:mm date strings are correctly parsed.
Use ISO date strings: yyyy-MM-dd HH:mm are also recognized.
Build the Date object yourself.
For the second option, since you only really care about the time, you could just split the time string yourself and pass them to Date.setHours(h, m, s):
var timeParts = $('#starttime').val().split(':', 2);
var time1 = new Date();
time1.setHours(timeParts[0], timeParts[1]);
You are experiencing an invalid time in your datestring. time1 is NaN, and so diff will be. It might be better to use this:
var date = new Date();
var match = /^(\d+):(\d+):(\d+)$/.exec($('#starttime').val()); // enforcing format
if (!match)
return alert("Invalid input!"); // abort
date.setHours(parseInt(match[1], 10));
date.setMinutes(parseInt(match[2], 10));
date.setSeconds(parseInt(match[3], 10));
var diff = Date.now() - date;
If you are trying to calculate the time difference between two dates, then you do not need to create a new date object to do that.
var time1 = new Date(dateString).getTime();
var time2 = new Date().getTime();
var diff = time1 - time2;// number of milliseconds
var seconds = diff/1000;
var minutes = seconds/60;
var hours = minutes/60;
Edit: You will want to take into account broofa's answer as well to
make sure your date string is correctly formatted
The getTime function returns the number of milliseconds since Jan 1, 1970. So by subtracting the two values you are left with the number of milliseconds between each date object. If you were to pass that value into the Date constructor, the resulting date object would not be what you are expecting. see getTime

Calculate the Date based on Current Date and No of Days using Javascript/Jquery

I need a help..
I have a Current Date and No of days column.
When i enter number of days,i should add current date plus no of days entered.
For example,
todays date 5th jan + 20(no of days) = 25th Jan 2011 in another column.
Kindly help me.
Thanks in Advance.
Date.js is fantastic for this.
Date.today().add(5).days();
As you are learning JavaScript you may find the w3schools site useful for simple examples of objects and functions that are exposed and how they may be used.
http://www.w3schools.com/jsref/jsref_obj_date.asp
You can calculate the date as follows:
var d = new Date(); // Gets current date
var day = 86400000; // # milliseconds in a day
var numberOfDays = 20;
d.setTime(d.getTime() + (day*numberOfDays)); // Add the number of days in milliseconds
You can then use one of the various methods of displaying the date:
alert(d.toUTCString());
You could do something like
Date.today().add(X).days();
Where X is the number of days the user has entered.
You can add dates like this in js:
var someDate = new Date();
var numberOfDaysToAdd = 6;
someDate.setDate(someDate.getDate() + numberOfDaysToAdd);
var month = someDate.getMonth() + 1; //Add 1 because January is set to 0 and Dec is 11
var day = someDate.getDate();
var year = someDate.getFullYear();
document.write(month + "/" + day + "/" + year);
See this p.cambell's answer here: How to add number of days to today's date?

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