A somewhat non obvious scoping issue of javascripts callbacks

callback_scoping.js

function test() {
  for (var i=0;i < 5;i++) {
    console.log('orig: '+ i);
 
    // Crazy function with a callback here, making it async
    setTimeout(function () {
      // We might expect `i` to be whatever it was in the loop
      // when we called the setTimeout, but it's actually not evaluated
      // until the "callback" runs, and hence it will have the value
      // `i` had in that exact moment.
      console.log('cb: '+ i);
    }, 100);
  }
}
 
test();