Finding the sum of an array in javascript [duplicate]

Question

I have to write 6 small JavaScript scripts for school and I've got them all working apart from this one.

function calculate() {
    var numbers = [
        document.getElementById("num_one").value ,
        document.getElementById("num_two").value ,
        document.getElementById("num_three").value 
    ];
    var sum = numbers[0] + numbers[1] + numbers[2];
    document.getElementById("display_sum").innerHTML = sum;
}

The user is supposed to enter 3 numbers click a button and it should add them all togther or "find the sum".

My Problem is, it just joins the numbers togther instead of adding them. Does anyone know a way to fix this?

Answer 1

You are "summing" string variables so Javascript is concatenating them.

You need to convert them to numbers in order to have an arithmetic sum:

function calculate() {
        var numbers = [
            document.getElementById("num_one").value ,
            document.getElementById("num_two").value ,
            document.getElementById("num_three").value 
        ];
        var sum = Number(numbers[0]) + Number(numbers[1]) + Number(numbers[2]);
        document.getElementById("display_sum").innerHTML = sum;
        }