A javascript variable defined outside a function is 'undefined' within the function

Question

Why is MM_SYSTEM_RESTART_SECONDS undefined in the following snippet?

If var MM_SYSTEM_RESTART_SECONDS = 40; is put inside the function, then MM_SYSTEM_RESTART_SECONDS is 40, but if outside the function, then MM_SYSTEM_RESTART_SECONDS is always undefined.

var MM_SYSTEM_RESTART_SECONDS = 40;


function wait_until_MM_restarts()
{
    restart_timeout_start_seconds = get_cookie( "restart_timeout_start_seconds" )
    elapsed_restart_seconds =  elapsed_seconds( restart_timeout_start_seconds )
    append_debug_message( elapsed_restart_seconds + "/" +   MM_SYSTEM_RESTART_SECONDS )
    if( elapsed_restart_seconds > MM_SYSTEM_RESTART_SECONDS )

It shouldn't be. I can think of things that might cause that effect … but would have to see the rest of the function to tell. It is usually a good idea to provide snippets of code that can be run to demonstrate the problem. — Quentin
– Quentin, Commented Mar 7, 2012 at 0:13
I think you have to provide some more context. Better, create a jsfiddle.net demo. — Felix Kling
– Felix Kling, Commented Mar 7, 2012 at 0:14
I tend to avoid globals. I understand your interest in why this is happening, it's a good question (+1). However, I would pass MM_SYSTEM_RESTART_SECONDS into the wait_until_MM_restarts() function as a parameter. — Surreal Dreams
– Surreal Dreams, Commented Mar 7, 2012 at 0:20
Chances are pretty good that MM_SYSTEM_RESTART_SECONDS is defined in some other scope (inside some other function) and isn't available from this function because as you've shown it here, it would work just fine. — jfriend00
– jfriend00, Commented Mar 7, 2012 at 0:21
It seems to work with this attempt at a demo: jsfiddle.net/qUhQV I second @jfriend00's suggestion that there's a possibility it's a scope problem. — Jared Farrish
– Jared Farrish, Commented Mar 7, 2012 at 0:24

user1952338 · Accepted Answer · 2013-01-06 05:30:26Z

2

This just bit me. If you call the function before/above the variable declaration the variable might be undefined.

For example

f("before");

var value = 99;
function f(msg)
{    
  alert("msg=" + msg + " value=" + value);
}

f("after");

results in:

msg=before value=undefined
msg=after value=99

http://jsfiddle.net/qUhQV/4/

answered Jan 6, 2013 at 5:30

user1952338

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