Strange behaviour when adding day on Date

Question

I'm trying to add some day on a date but actually i got a strange result...

I test with today as current day (28/02/2019), and try to add like 400 day and I'm in year 2096... I think tere is a problem

Take a look at my function :

const user = { LastReport: new Date(), Validite: "413" }

var temp = new Date(user.LastReport)
console.log("Current : " + temp);
user.DateValide = temp.setDate(temp.getDate() + user.Validite);
console.log("Day to add : " + user.Validite)
console.log("Result : " + new Date(user.DateValide))

and my result :

There is something i'm doing wrong ?

Possible duplicate of [Add days to JavaScript Date](https://stackoverflow.com/questions/563406/add-days-to-javascript-date) — CodeF0x, Feb 28 '19 at 10:30
..... Yes a saw a lot of topic about add a day on a date. But actually my code look like the same as the others topic and it still don't works — Toto NaBendo, Feb 28 '19 at 10:32
Aha `413` is a string. Check the answer posted. Please create a [mcve] from next time — adiga, Feb 28 '19 at 10:35

score 5 · Accepted Answer · answered Feb 28 '19 at 10:33

The temp.getDate() + user.Validite are being concatenated as strings so the days added is 28413 instead of 441.

Use parseInt() to convert them to Number or you can prefix them with an arithmetic operator like +.

const user = { LastReport: new Date(), Validite: "413" }

var temp = new Date(user.LastReport)
console.log("Current : " + temp);
//user.DateValide = temp.setDate(parseInt(temp.getDate()) + parseInt(user.Validite));
user.DateValide = temp.setDate(+temp.getDate() + +user.Validite);
console.log("Day to add : " + user.Validite)
console.log("Result : " + new Date(user.DateValide))

In ECMAScript, the '+' character is overloaded and has three possible meanings. When used like `+ +user.Validite`, the first is seen as the [*addition operator*](http://ecma-international.org/ecma-262/9.0/#sec-addition-operator-plus), the second is seen as the [*unary + operator*](http://ecma-international.org/ecma-262/9.0/#sec-unary-plus-operator). :-) — RobG, Mar 02 '19 at 21:27

Strange behaviour when adding day on Date

1 Answers1