editing value of inputfield using Javascript

Question

So I have this code:

function resetAll(einde) {
if(einde !=1) {
    if(beurt == 0) {
        spelerbolletje.gewonnen += 1;
        document.getElementById("bolletje").value = spelerbolletje.gewonnen;
    } else {
        spelerkruisje.gewonnen += 1;
        document.getElementById("kruisje").value = spelerkruisje.gewonnen;
    }
    }
    setVakjes();
    resetVakjes();
}

somehow this sets the value for the value of the winner from 0 to NaN. does someone know how to solve this?

Check out Shitsu's answer. Incrementing a variable that has not been defined would not work correctly. — Thomas
– Thomas, Commented Jan 22, 2016 at 11:04

Derlin · Accepted Answer · 2016-01-22 11:02:30Z

1

What you do seems correct. I think the problem is that XX.gewonnen has not been initialized.

var a = {};
a.gewonnen += 1; // => gewonnen = NaN

So, ensure gewonnen is defined:

if(XX.gewonnen == undefined) XX.gewonnen = 0;
// rest of your code

answered Jan 22, 2016 at 11:02

Derlin

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5 Comments

Grey Over a year ago

all needed variables are declared at the top of the document or when they are needed, so XX.gewonnen has been declared at the top since XX is needed all over the document

Thomas Over a year ago

Is it declared like XX.gewonnen;, or is it given the value 0 like XX.gewonnen = 0;?

Grey Over a year ago

function fSpeler(naam, beurt, gewonnen) { this.naam = naam; this.beurt = beurt; this.gewonnen = gewonnen; }

Grey Over a year ago

nevermind, thanks, it was indeed because XX.gewonnen was not given a value at the beginning, thank :D

Thomas Over a year ago

That's cool and all, but is it, at some point, actually given a value? If it is only declared as XX.gewonnen;, then it is simply a place in memory where a value can be stored. If it's declared as XX.gewonnen = 0;, then JavaScript knows that the value is numeric, so it can be incremented. EDIT: Ah okay, graag gedaan!

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