Why Does Removing Duplicates from a JavaScript Array Fail with Zero?

Removing Duplicates from a JavaScript Array: The Mysterious Zero Error

When working with arrays in JavaScript, it's often essential to ensure that values are unique. However, encountering an error when dealing with zero values can be perplexing. Let's explore the issue and its solution.

The provided code snippet employs the Array.prototype.getUnique function to eliminate duplicates:

Array.prototype.getUnique = function() {
 var o = {}, a = [], i, e;
 for (i = 0; e = this[i]; i++) {o[e] = 1};
 for (e in o) {a.push (e)};
 return a;
}

While this function works flawlessly in most cases, it stumbles when the array contains a zero. To resolve this issue, we can leverage the native filter method of an Array introduced in JavaScript 1.6/ECMAScript 5:

function onlyUnique(value, index, array) {
  return array.indexOf(value) === index;
}

// usage example:
var a = ['a', 1, 'a', 2, '1'];
var unique = a.filter(onlyUnique);

console.log(unique); // ['a', 1, 2, '1']

In this solution, the onlyUnique function ensures that each value appears only once in the resulting array. When used with the filter method, it effectively removes duplicates, including zero.

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