在内部JavaScript回调函数中访问父函数参数的正确方法

Question

Take the following code snippet.

var exec = require('child_process').exec;

var extraInfo = {'test':1,'passing':'test'};

runWithData(extraInfo);

function runWithData(passedData)
{
    exec('/Users/test/Desktop/testcommand', function callback(error,stdout,stderr)
    {
        if (error)
        {
            console.log("ERROR",stderr);
        }
        else
        {
            console.log(stdout);
        }
    });
}

Within the callback of exec I want to be able to access the passedData. Is accessing passedData direct the correct way to do this and will this get overwritten if multiple function calls are being processed at the same time, or is there a way to attach the info into the callback function so it is tied to it?

Answer 1

From @jfriend00:

You can just access 'passedData' directly. It's in a parent scope which is completely accessible to you in the callback. Each function call creates a new scope and thus creates a new set of data so multiple function calls do not mess it up

See also: MDN Closures

[Note: Marked community wiki as this is mostly from others' comments, etc, for which I do not claim point credit. Feel free to edit and improve]