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

Question

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?

Answer 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.

Answer 2

the simplest:

dots = dots*1+5; 

the dots will be converted to number.