I've seen this in a few places
function fn() {
return +new Date;
}
And I can see that it is returning a timestamp rather than a date object, but I can't find any documentation on what the plus sign is doing.
Can anyone explain?
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Possible duplicate of What is the purpose of a plus symbol before a variable?– Donald DuckCommented Aug 8, 2018 at 23:16
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7 Answers
That's the + unary operator. It's equivalent to:
function(){ return Number(new Date); }
answered Oct 21, 2008 at 11:49
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4But like why wouldn't you use the defined
getTimemethod on the date object?!– tkoneCommented Aug 23, 2012 at 21:36 -
34Under almost no circumstances should you actually use this. I just really got burnt on this. +new Date() in addition to any kind of mathematical operations will undergo a major performance penalty.– GeuisCommented Oct 11, 2012 at 0:58
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13@BradKoch in programming brevity is most certainly not the wit of the soul. As the python community has so adequately put it "explicit is always better than implicit." What if a browser changed the automatic type conversion that's implied there through a regression? Now your code just doesn't work!
.getTime()will always insure it does.– tkoneCommented Oct 11, 2012 at 2:13 -
13@Geuis another excellent reason that just because you can doesn't meant you should!– tkoneCommented Oct 11, 2012 at 2:13
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16Sine ECMAScript 5 there is
Date.now(), which is the preferred way to get the date and time in milliseconds. Commented Feb 22, 2013 at 12:18
JavaScript is loosely typed, so it performs type coercion/conversion in certain circumstances:
http://blog.jeremymartin.name/2008/03/understanding-loose-typing-in.html
http://www.jibbering.com/faq/faq_notes/type_convert.html
Other examples:
>>> +new Date()
1224589625406
>>> +"3"
3
>>> +true
1
>>> 3 == "3"
true
answered Oct 21, 2008 at 11:47
A JavaScript date can be written as a string:
Thu Sep 10 2015 12:02:54 GMT+0530 (IST)
or as a number:
1441866774938
Dates written as numbers, specifies the number of milliseconds since January 1, 1970, 00:00:00.
Coming to your question it seams that by adding '+' after assignment operator '=' , converting Date to equal number value.
same can be achieve using Number() function, like Number(new Date());
var date = +new Date(); //same as 'var date =number(new Date());'
Here is the specification regarding the "unary add" operator. Hope it helps...
answered Oct 21, 2008 at 12:11
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2Link-only answers are not considered valuable on SO. This is a great example of why. It's defunct. Commented Mar 3, 2022 at 13:50
If you remember, when you want to find the time difference between two dates, you simply do as follows:
var d1 = new Date("2000/01/01 00:00:00");
var d2 = new Date("2000/01/01 00:00:01"); //one second later
var t = d2 - d1; //will be 1000 (msec) = 1 sec
typeof t; // "number"
Now if you check type of d1-0, it is also a number:
t = new Date() - 0; //numeric value of Date: number of msec's since 1 Jan 1970.
typeof t; // "number"
That + will also convert the Date to Number:
typeof (+new Date()) //"number"
But note that 0 + new Date() will not be treated similarly! It will be concatenated as string:
0 + new Date() // "0Tue Oct 16 05:03:24 PDT 2018"
answered Oct 16, 2018 at 12:07
It is a unary add operator and also used for explicit Number conversion, so when you call +new Date(), it tries to get the numeric value of that object using valueOf() like we get string from toString()
new Date().valueOf() == (+new Date) // true
answered Sep 18, 2016 at 8:40
It does exactly the same thing as:
function(){ return 0+new Date; }
that has the same result as:
function(){ return new Date().getTime(); }
answered Oct 21, 2008 at 11:48
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11Nope on 0+new Date. That first converts the date to a string and then prepends a "0", (eg: "0Tue Oct 21 2008 20:38:05 GMT-0400"); Commented Oct 22, 2008 at 0:40
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