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javascriptstringmathaddition

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?

Solution

  • 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.