Not adding 2 numbers correctly in javascript [duplicate]

Question

i have a drop down list in my html with values show here,

<select id="thedropdown">
<option value="1">test1</option>
<option value="2" selected="selected">test2</option>
<option value="3">test3</option>
</select>

And my javascript:

function myFunction()
{
var a = document.getElementById("thedropdown");
var b = a.options[a.selectedIndex].value;

var y=b;
var x=y+2;
var demoP=document.getElementById("demo")
demoP.innerHTML= x;
}

However the answer when i click the button makes it 22 when it should be 4. you can see my problem. Cheers for help in advance

Probably because b is a string, and thence y, and thence you are converting the number 2 to a string and tacking it on the end of the first "2" string — Xitalogy
– Xitalogy, Commented Feb 9, 2013 at 16:51

Matt Ball · Accepted Answer · 2013-02-10 00:14:44Z

6

Right now your code concatenates strings. You need to parseInt() or parseFloat() (or Number() or +) the values before adding.

When using parseInt() make sure to always specify the second argument (the radix):

b = parseInt(a.options[a.selectedIndex].value, 10);

edited Feb 10, 2013 at 0:14

answered Feb 9, 2013 at 16:50

Matt Ball

361k102 gold badges655 silver badges725 bronze badges

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

2 Comments

user2057440 Over a year ago

so do i have to create a new var for that like var c = parseInt(b)?

Matt Ball Over a year ago

That would work, as would b = parseInt(b).

Plynx · Accepted Answer · 2013-02-09 16:52:58Z

3

You can use unary + to convert numeric string to a number:

var y=+b;

or

var x=+y+b;

answered Feb 9, 2013 at 16:52

Plynx

11.5k3 gold badges34 silver badges34 bronze badges

Comments

mika · Accepted Answer · 2013-02-09 16:50:43Z

2

You are concatenating a string instead of adding numbers:

var x=y+2;

Try that:

var x=parseInt(y)+2;

answered Feb 9, 2013 at 16:50

mika

1,4611 gold badge12 silver badges23 bronze badges

Comments

Mickael · Accepted Answer · 2013-02-09 16:50:39Z

0

You have to convert your values with parseInt function:

    var y = parseInt(b, 10) + 2;

answered Feb 9, 2013 at 16:50

Mickael

5,7362 gold badges28 silver badges23 bronze badges

Comments

Tapan Nallan · Accepted Answer · 2013-02-09 16:58:40Z

0

If one of the operands is a string , + operator performs concatenation.

this will work

function myFunction()
{
  var a = document.getElementById("thedropdown");
  var b = a.options[a.selectedIndex].value;

  var y=b;
  var x= parseInt(y) + 2;
  var demoP=document.getElementById("demo")
  demoP.innerHTML= x;
}

Note var x= parseInt(y) + 2;

answered Feb 9, 2013 at 16:58

Tapan Nallan

1,8523 gold badges20 silver badges37 bronze badges

Collectives™ on Stack Overflow

Not adding 2 numbers correctly in javascript [duplicate]

5 Answers 5

2 Comments

Comments

Comments

Comments

Comments

Linked

Hot Network Questions

Collectives™ on Stack Overflow

5 Answers 5

2 Comments

Comments

Comments

Comments

Comments

Linked

Related