Global footprint

If you are developing a module, which might be running on a web page, which also runs other modules, then you must beware of the variable name overlapping.

Suppose we are developing a counter module:

let myCounter = {
  number: 0,
  plusPlus: function () {
    this.number = this.number + 1;
  },
  isGreaterThanTen: function () {
    return this.number > 10;
  },
};

Note: this technique is often used with closures, to make the internal state immutable from the outside.

The module now takes only one variable name — myCounter. If any other module on the page makes use of such names like number or isGreaterThanTen then it's perfectly safe because we will not override each other's values;