javascript - "a.getFullYear is not a function" when trying to get date difference - Stack Overflow

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I'm trying to get a date difference between a date and today with JS. Here is my code, but I get "a.getFullYear is not a function".

var brbr = '<br><br>';
var duedate="2015-11-06";
document.write(duedate);
document.write(brbr);

// Today's date:
var today = new Date();
var dd = today.getDate();
var mm = today.getMonth()+1; //January is 0!
var yyyy = today.getFullYear();

if(dd<10) {
    dd='0'+dd
} 

if(mm<10) {
    mm='0'+mm
} 
today = yyyy+'-'+mm+'-'+dd;
document.write(today);
document.write(brbr);

// DIFFERENCE 2 dates:
var _MS_PER_DAY = 1000 * 60 * 60 * 24;


// a and b are javascript Date objects
function dateDiffInDays(a, b) {
    // Discard the time and time-zone information.
    var utc1 = Date.UTC(a.getFullYear(), a.getMonth(), a.getDate());
    var utc2 = Date.UTC(b.getFullYear(), b.getMonth(), b.getDate());
    return Math.floor((utc2 - utc1) / _MS_PER_DAY);
}

Result:

var days_left = dateDiffInDays(today, duedate);
document.write(days_left);
document.write(brbr);

I'm trying to get a date difference between a date and today with JS. Here is my code, but I get "a.getFullYear is not a function".

var brbr = '<br><br>';
var duedate="2015-11-06";
document.write(duedate);
document.write(brbr);

// Today's date:
var today = new Date();
var dd = today.getDate();
var mm = today.getMonth()+1; //January is 0!
var yyyy = today.getFullYear();

if(dd<10) {
    dd='0'+dd
} 

if(mm<10) {
    mm='0'+mm
} 
today = yyyy+'-'+mm+'-'+dd;
document.write(today);
document.write(brbr);

// DIFFERENCE 2 dates:
var _MS_PER_DAY = 1000 * 60 * 60 * 24;


// a and b are javascript Date objects
function dateDiffInDays(a, b) {
    // Discard the time and time-zone information.
    var utc1 = Date.UTC(a.getFullYear(), a.getMonth(), a.getDate());
    var utc2 = Date.UTC(b.getFullYear(), b.getMonth(), b.getDate());
    return Math.floor((utc2 - utc1) / _MS_PER_DAY);
}

Result:

var days_left = dateDiffInDays(today, duedate);
document.write(days_left);
document.write(brbr);

• javascript
• date

Share Improve this question Follow edited Nov 4, 2015 at 1:09 Lee Taylor 7,9841616 gold badges3737 silver badges5353 bronze badges asked Nov 4, 2015 at 1:06 mesqueebmesqueeb 6,38477 gold badges5252 silver badges8585 bronze badges

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2 Answers 2

Sorted by: Reset to default 2

You need to convert today and duedate into Date() objects in order to use .getFullYear()

function dateDiffInDays(a, b) {
    var aDate = new Date(a);
    var bDate = new Date(b);

    // Discard the time and time-zone information.
    var utc1 = Date.UTC(aDate.getFullYear(), aDate.getMonth(), aDate.getDate());
    var utc2 = Date.UTC(bDate.getFullYear(), bDate.getMonth(), bDate.getDate());
    return Math.floor((utc2 - utc1) / _MS_PER_DAY);
}

What I did was:

var a = Date.parse("date");
var b = new Date(a);

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