How to add two strings as if they were numbers? [duplicate]

Answer 1

You can use parseInt to parse a string to a number. To be on the safe side of things, always pass 10 as the second argument to parse in base 10.

num1 = parseInt(num1, 10);
num2 = parseInt(num2, 10);
alert(num1 + num2);

Answer 2

I would use the unary plus operator to convert them to numbers first.

+num1 + +num2;

Answer 3

I've always just subtracted zero.

num1-0 + num2-0;

Granted that the unary operator method is one less character, but not everyone knows what a unary operator is or how to google to find out when they don't know what it's called.

Answer 4

document.getElementById(currentInputChoosen).value -= +-100;

Works in my case, if you run into the same problem like me and can't find a solution for that case and find this SO question.

Sorry for little bit off-topic, but as i just found out that this works, i thought it might be worth sharing.

Don't know if it is a dirty workaround, or actually legit.

Answer 5

Try this if you are looking for simple Javascript code and want to use two input box and add numbers from the two value. Here's the code.

    Enter the first number: <input type="text" id="num1" /><br />
    Enter the seccond number: <input type="text" id="num2" /><br />
    <input type="button" onclick="call()" value="Add"/>

    <script type="text/javascript">
    function call(){
    var q=parseInt(document.getElementById("num1").value);
    var w=parseInt(document.getElementById("num2").value);
    var result=q+w;
    }
    </script>

for more details please visit http://informativejavascript.blogspot.nl/2012/12/javascript-basics.html

Answer 6

MDN docs for parseInt
MDN docs for parseFloat

In parseInt radix is specified as ten so that we are in base 10. In nonstrict javascript a number prepended with 0 is treated as octal. This would obviously cause problems!

parseInt(num1, 10) + parseInt(num2, 10) //base10
parseFloat(num1) + parseFloat(num2)

Also see ChaosPandion's answer for a useful shortcut using a unary operator. I have set up a fiddle to show the different behaviors.

http://jsfiddle.net/EtX6G/

var ten = '10';
var zero_ten = '010';
var one = '1';
var body = document.getElementsByTagName('body')[0];

Append(parseInt(ten) + parseInt(one));
Append(parseInt(zero_ten) + parseInt(one));
Append(+ten + +one);
Append(+zero_ten + +one);

function Append(text) {
    body.appendChild(document.createTextNode(text));
    body.appendChild(document.createElement('br'));
}