Can't use variables outside of function in javascript

Question

I recently started to learn Javascript and have prior experience in server side languages such as PHP. The issue I'm having is that I cannot use variables that are defined outside of a function inside the function. I always have to copy the variable into the function in order to get my code to work. I will post an example below.

    var first = document.getElementById("first");
    var second = document.getElementById("second");

    function add () {
        alert(Number(first.value) + Number(second.value));
    }

I am trying to understand why I cannot use functions that are defined outside the function inside of it. In order to use the functions I have to copy them into the function otherwise it does not run. — Joe Scotto
– Joe Scotto, Commented May 31, 2014 at 14:48
How do you expect to use a variable inside the function if you don't write its name? — Oriol
– Oriol, Commented May 31, 2014 at 14:48
Variable scoping rules apply as normal, so that code should be fine. But some things to consider: are you calling add before the variables are set, and do those elements actually exist and have a value? — Dave
– Dave, Commented May 31, 2014 at 14:48
I just realized that my <script> tags are called in the <head> which would explain this. Stupid question and I will delete it soon. — Joe Scotto
– Joe Scotto, Commented May 31, 2014 at 14:50

lrn · Accepted Answer · 2014-05-31 14:49:18Z

2

Most likely the problem is that your script is being executed when the page is still being loaded, and before the "first" and "second" elements have been created.

Accessing the variables works fine. They just happen to be initialized to "undefined" at the time they are created. Moving the variables inside the function means that they aren't initialized until the function is called, which is after the page has been completely loaded.

answered May 31, 2014 at 14:49

lrn

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Joe Scotto Over a year ago

I just realized this and will accept your answer as soon as possible

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