How to understand the moment of solving a problem in JS?

Question

JavaScript

Again, not a very clear moment in solving a problem in JS.
Task :
Let strings be an array of strings.
Write a unique(strings) function that returns an array containing only the unique elements of arr.
Decision:

function enique(arr) {
  var obj = {};

  for (var i = 0; i < arr.length; i++) {
    var str = arr[i];
    obj[str] = true;
  }

  return Object.keys(obj);
}

var strings = [1, 1, 1, 1, 1, 2, 3, 4, 5, 4, 4, 4, 4];

console.log( enique(strings) );

And so this line obj[str] = true is not so clear here; Explain, please.

Answer 1

An associative array is created with strings as keys. Since the keys in such an array are unique, when a repeated row occurs in the source data, a new element of the obj array is not created, but simply overwritten by the previously created one. The result of the work of the subroutine is an array of keys of the obj array, which are unique strings.

Answer 2

strings.reduce(function(p, v) {
  if (-1 === p.indexOf(v)) {
    p.push(v); 
  } 
  return p; 
}, []);

Answer 3

The programmer does not know how to Set, so he uses an associative container.