People Function in ES5

people-function-in-es5.js

function People() {
  var self = this; // Some choose `that` instead of `self`.
  self.size = 0;

  setInterval(function addMorePeople() {
    // The callback refers to the `self` variable of which
    // the value is the expected object.
    self.size++;
  }, 1000);
}