Javascript does not sum numbers

Question

I'm not good using javascript/jquery so this is a dumb question! I coded this

    <li>
        <a href="http://www.mazzodifiori.it/fiori/P15-Ficus.jpg"><img src="http://www.mazzodifiori.it/fiori/P15-Ficus.jpg" width=50 height=50 /></a>
        <br><input name="p1" value="p1" prezzo="5" type="checkbox" />
        <br><label>Pianta &euro;</label><span class="price">5</span>
    </li>

    <li>
        <a href="http://www.mazzodifiori.it/fiori/P15-Ficus.jpg"><img src="http://www.mazzodifiori.it/fiori/P15-Ficus.jpg" width=50 height=50 /></a>
        <br><input name="p2" value="p2" prezzo="3" type="checkbox" />
        <br><label>Pianta &euro;</label><span class="price">3</span>
    </li>

var checkValues = $('input[type=checkbox]:checked').map(function() {
    return $(this).attr('prezzo');
}).get();

for(var i=0;i<checkValues.length;i++) {
    var tot = tot + checkValues[i];
    alert(tot);
}

In this way checkvalues contains array of numbers. So checking that 2 checkbox for example, on the browser appear 2 alert:

undefined5

and

undefined53

like if javascript is concatenating numbers like they would be strings!

how can i solve this?

var tot = tot + checkValues[i]; - the tot on right hand side is not initialized . hence the result. Put the declaration outside the loop var tot=0; — karthikr
– karthikr, Commented Jun 11, 2014 at 14:55
Why do you think checkValues contains an array of numbers? Have you read the documentation for .attr()? It always returns a string (or undefined). — Ian
– Ian, Commented Jun 11, 2014 at 14:55
watch this exception Cannot read property 'map' of null, seems the problem is that map function recieves null or undefined values from checkboxes — martinezjc
– martinezjc, Commented Jun 11, 2014 at 15:00
You should change this for(var i=0;i<checkValues.length;i++) { var tot = tot + checkValues[i]; alert(tot); } to this: var i,tot=0; for(i=0;i<checkValues.length;i++) { tot = tot + +checkValues[i]; alert(tot); }. Javascript doesn't have block scope - so it's less confusing if you write it outside of the for block. Also, you should initialize tot to zero because in the first iteration tot's value is undefined — thedude
– thedude, Commented Jun 11, 2014 at 15:08

thedude · Accepted Answer · 2014-06-11 14:55:46Z

3

Try to change:

var tot = tot + checkValues[i];

to this:

var tot = tot + +checkValues[i];

OR

change this:
return $(this).attr('prezzo');

to this:

return +$(this).attr('prezzo');

This will coerce the string to a number

answered Jun 11, 2014 at 14:55

thedude

3551 gold badge3 silver badges12 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

hlscalon · Accepted Answer · 2014-06-11 14:55:36Z

2

Check this out:

var tot = 0;
for(var i=0;i<checkValues.length;i++) {
    tot = tot + parseInt(checkValues[i]);
    alert(tot);
}

answered Jun 11, 2014 at 14:55

hlscalon

7,6004 gold badges35 silver badges41 bronze badges

2 Comments

Giacomo Cerquone Over a year ago

I fix it following your "tot = tot + parseInt(checkValues[i]);" and the advice that gave me raligan! I'm very happy I fixed my problem!! THANK YOU :DDD PS=I tried to use parseInt but it didn't function... maybe I was doing it wrong!

user193130 Over a year ago

@GiacomoCerquone Alternatively, you could use for(var i=0, tot=0;i<checkValues.length;i++) {

Isaac · Accepted Answer · 2014-06-11 14:54:53Z

1

You keep reinitializing tot (which isn't strictly speaking a problem in JS, but it's bad form), plus you're initializing it to undefined initially, since you're defining it as itself. Initialize it to 0 before the loop.

answered Jun 11, 2014 at 14:54

Isaac

3542 gold badges4 silver badges13 bronze badges

2 Comments

Ian Over a year ago

While this fixes the undefined problem, it will still do string concatentation, not addition

Giacomo Cerquone Over a year ago

it's anyway an error from me. Thank you, I'm fixing it :)

user4593252 · Accepted Answer · 2014-06-11 14:55:48Z

1

Javascript is a duck typed (loosely typed) language. If it thinks they're strings, it'll concat them. Try forcing them into the data type you need. If they're integers, use parseInt(varName) + parseInt(varName2).

http://www.w3schools.com/jsref/jsref_parseint.asp

answered Jun 11, 2014 at 14:55

user4593252

3,5168 gold badges33 silver badges58 bronze badges

1 Comment

user4593252 Over a year ago

If on of the variables is "undefined," parseInt won't be able to parse it because undefined is not a number. Check to see if your values are numbers by using IsNaN(var1) before parsing.

Collectives™ on Stack Overflow

Javascript does not sum numbers

4 Answers 4

Comments

2 Comments

2 Comments

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

4 Answers 4

Comments

2 Comments

2 Comments

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related