How can i use external variables in "setInterval" code?

[Lagon666]

When i run this functions it says the count is undefined.

function hello(){
    var count = 0;
    var timer = setInterval('count+=1;alert(count);',2000);
}
 

[Dormilich]

some functions change the variable scope. setInterval() and setTimeout() will have global scope and because count was defined inside a function, count will have the function's local scope and not the global one. thus count is undefined (on global scope).

to work around that you need two things, a function for the code to execute and a closure to preserve the values.

(will be back when I got more time…)

[rnd me]

function hello(){
    var count = 0;
    var timer = setInterval( function(){  count+=1;alert(count); },2000);
}
 

[Dormilich]

some articles about closures:
JavaScript Closures for Dummies
JavaScript Closures 101
JavaScript Closures

and some about Scope
Scope in JavaScript
Explaining JavaScript Scope and Closures