How to force JS to do math instead of putting two strings together

How to force JS to do math instead of putting two strings together

I need javascript to add 5 to an integer variable, but instead it treats the variable as a string, so it write out the variable, then add 5 onto the end of the “string”. How can I force it to do math instead?
var dots = document.getElementById(“txt”).value; // 5
function increase(){
dots = dots + 5;
}

Output: 55
How can I force it to output 10?

Solutions/Answers:

Solution 1:

You have the line

dots = document.getElementById("txt").value;

in your file, this will set dots to be a string because the contents of txt is not restricted to a number.

to convert it to an int change the line to:

dots = parseInt(document.getElementById("txt").value, 10);

Note: The 10 here specifies decimal (base-10). Without this some browsers may not interpret the string correctly. See MDN: parseInt.

Solution 2:

the simplest:

dots = dots*1+5;

the dots will be converted to number.

Solution 3:

DON’T FORGET – Use parseFloat(); if your dealing with decimals.

Solution 4:

I’m adding this answer because I don’t see it here.

One way is to put a ‘+’ character in front of the value

example:

var x = +'11.5' + +'3.5'

x === 15

I have found this to be the simplest way

In this case, the line:

dots = document.getElementById("txt").value;

could be changed to

dots = +(document.getElementById("txt").value);

to force it to a number

NOTE:

+'' === 0
+[] === 0
+[5] === 5
+['5'] === 5

Solution 5:

parseInt() should do the trick

var number = "25";
var sum = parseInt(number, 10) + 10;
var pin = number + 10;

Gives you

sum == 35
pin == "2510"

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

Note: The 10 in parseInt(number, 10) specifies decimal (base-10). Without this some browsers may not interpret the string correctly. See MDN: parseInt.

Solution 6:

This also works for you:

dots -= -5;