Why does the Date class return NaN?

Question

Getting strange results when converting a timestamp to readable date.

var date = new Date(x);

console.log(x);

showTooltip(item.pageX, item.pageY, (date.getMonth()+1)+"-"+date.getDate()+"-"+date.getFullYear()+" / "+y );

The console shows for example '1404792000000' so the timestamp is good, but the output results in 'NaN-NaN-NaN / 864'.

What am I doing wrong here?

Not enough code is presented. Where do x, item.pageX, item.pageY all come from and are they correct, and are they the arguments wanted by showTooltip() function. You are correct x is a number. — Wayne, Jul 13 '14 at 08:05
Reason: `new Date('1404792000000')` -> Invalid Date, so all the accessors return NaN — user2864740, Jul 13 '14 at 08:16
@user2864740 I'm assumeing the '' are not actually part of the value of x. If it were then the source would be something like x = "'1404792000000'"; or a string with quotes in the string. — Wayne, Jul 13 '14 at 08:26
@Wayne Any string which is not recognized/supported as per Date.parse will result in such an "Invalid Date" object, it need not contain quotes in it although that is a pretty good way to make it invalid. — user2864740, Jul 13 '14 at 08:49

score 3 · Accepted Answer · edited May 23 '17 at 12:11

3

Verify x with typeof function like this :

console.log(typeof x);

X must to be an number (int) if is an timestamp (like this 1404792000000), use parseInt() function if x is a string.

var date = new Date(parseInt(x));

showTooltip(item.pageX, item.pageY, (date.getMonth()+1)+"-"+date.getDate()+"-"+date.getFullYear()+" / "+y );

Example :

date = new Date("1404792000000"); // String : Date {Invalid Date}

date = new Date(1404792000000); // Integer : Date {Tue Jul 08 2014 ...}

date = new Date(parseInt("1404792000000")); // Str to int : Date {Tue Jul 08 2014 ...}

Without parseInt, use the calculator operator. (@RobG comment)

Like this :

date = new Date(+"1404792000000"); // Str to int

Which is better to use for a calculator parseInt() or eval() in Javascript?

edited May 23 '17 at 12:11

Community

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answered Jul 13 '14 at 08:13

user2226755

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"X must to be an integer" is a bit misleading. I think you meant to say "to be treated as a [*time value*](http://ecma-international.org/ecma-262/5.1/#sec-15.9.1.1), *x* must be a String", otherwise it will be passed to [*Date.parse*](http://ecma-international.org/ecma-262/5.1/#sec-15.9.4.2) which will attempt to parse it as a date and time. Since "1404792000000" is not a valid date and time string, *Date.parse* will return `NaN`. It's not really necessary to test the value, just apply parseInt anyway (or to be more concise, use the unary `+` operator: `d = new Date(+x)`). – RobG Jul 13 '14 at 08:32
Thank you for your constructive comment. – user2226755 Jul 13 '14 at 08:42

score 1 · Answer 2 · answered Jul 13 '14 at 08:17

The reason is that new Date('1404792000000') results in an "Invalid Date" object, so all the access methods (e.g. getMonth) return NaN. This is because the date constructor does not accept a string representing the epoch milliseconds.

Compare with new Date(1404792000000), which is "Mon Jul 07 2014 21:00:00 GMT-0700 (Pacific Daylight Time)". Note how a number was specified.

Why does the Date class return NaN?

2 Answers2

Example :

Without parseInt, use the calculator operator. (@RobG comment)