Async Loop Pitfall

gistfile1.js

// the following code outputs: 999999999

var someArray = [1,2,3,4,5,6,7,8,9];

for(var i=0 ; i<someArray.length ; i++) {

  performSomeAsyncOperation("foo", function hereIsACallback() {
    console.log(someArray[i]);
  });
}

One way to avoid this:

// the following code outputs: 123456789

var someArray = [1,2,3,4,5,6,7,8,9];

for(var i=0 ; i<someArray.length ; i++) {
  (function looper(i) {
    performSomeAsyncOperation("foo", function hereIsACallback() {
      console.log(someArray[i]);
    });
  })(i);
}