Javascript Closure practice

closure.js

/* jshint node: true */

var assert = require("assert");


/*
 * fn
 *
 * @return {Function}
 */

function fn() {
  var i = 0;

  return function(val) {
    if (val) {
      i = val;
    } else {
      return i;
    }
  };
}


describe("closures", function() {
  it("has isolated scopes", function() {
    var a = fn();
    var b = fn();

    a(1);
    b(2);
    assert(a() === 1);
    assert(b() === 2);

    b(3);
    assert(a() !== 3);
    assert(a() === 1);

    a(4);
    assert(b() !== 4);
    assert(b() === 3);
  });
});