Passing argument to setTimeout in a for loop

I'm trying to learn how to pass an argument to setTimeout in a javacript for loop. Here is the example code. As it is currently written, setTimeout is passed the same exact i each time, not reflecting the different i's that are actually in the array.

var a=100;
for (i i开发者_开发百科n array)
{   
    setTimeout("do_stuff(i, a)"), 2000);    
}

(I've seen somewhat similar questions and answers here, but the code examples are much more complicated. Answering this most basic example could much help others with the same problem. Thanks!!!)

To use a string (which you shouldn't do), you 'd need to do this:

var a=100;
for (i in array)
{   
    setTimeout("do_stuff(" + i + ", a)"), 2000);    
}

A better answer would be to scope the i variable in a new function invocation, which returns an anonymous function to give to setTimeout().

function do_stuff( i, a ) {
    return function() {
        // do something with i and a
    }
}

var a=100;
for (i in array)
{   
    setTimeout(do_stuff( i , a ), 2000);    
}

Now do_stuff() returns a function that has a scoped reference to a new i and a variable. Because each call to do_stuff will have its own scope, the function you return will reference the correct values.

EDIT: Off topic, but if array is actually an Array, then you really shouldn't use for-in because that's meant for enumeration. With an Array, you typically want iteration of numeric indices, and as such should use a standard for loop.