JavaScript - Why different output from if/else statement while using a variable declared before the statement? [duplicate]

Question

My question is about the following code:

var d = new Date();
var weekday = ["su", "mo", "tu", "we", "th", "fr", "sa"];
var deliver = weekday[d.getDay()];

if(condition){
    if(d.getDay() == 1){
       d.setHours(d.getHours() + 24); // adds a day
    }
    if(d.getUTCMonth() == 0 && d.getUTCDate() == 1){
        // do something
    } else {
        // version 1 or version 2
    }
}

//version 1: var deliver = weekday[d.getDay()];
//           document.getElementById("leverdatum").innerHTML = deliver;

//version 2: document.getElementById("leverdatum").innerHTML = deliver;;

Why, if I use version 1, the output is "tu" and if I use version 2 the output is "mo"?

Because of this? d.setHours(d.getHours() + 24); // adds a day. You shouldn't put var inside block-statements becuase of variable hosting, that might take away some of the confusion. — Halcyon
– Halcyon, Commented Mar 7, 2016 at 13:04
Version 1 & Version 2 — Removing that var makes no difference. — Quentin
– Quentin, Commented Mar 7, 2016 at 13:04
I think there's more to this than you're showing - how are you seeing this output? The additional var there won't make any difference, it's in the same scope. — James Thorpe
– James Thorpe, Commented Mar 7, 2016 at 13:05
If condition is false it doesn't do the +24h. I think that's what OP means. — Halcyon
– Halcyon, Commented Mar 7, 2016 at 13:05
Yeah, I don't really understand. What did you expect deliver; to do? — JJJ
– JJJ, Commented Mar 7, 2016 at 13:17

Quentin · Accepted Answer · 2016-03-07 13:21:05Z

1

The presence (or lack thereof) of var on that line does absolutely nothing.

The significant part is = weekday[d.getDay()];.

Because it is (at the time of writing) Monday, d.setHours(d.getHours() + 24); // adds a day will add a day. Making the day Tuesday.

But if you don't convert the value of d into a day and assign it to deliver after you change the value of d, then you will continue to have the original string.

answered Mar 7, 2016 at 13:21

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Quentin

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1 Comment

remkovdm Over a year ago

Thanks for understanding my question!

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