How Can I Efficiently Remove Duplicate Values from a JavaScript Array, Including Zero?

Identifying Duplicates in JavaScript Arrays with Prototype

In JavaScript, it's often necessary to remove duplicate values from arrays. One popular approach involves extending the Array prototype with a custom 'getUnique' function, as seen below:

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;
}

However, this script encounters issues when the array contains a zero value. To understand why, let's examine the problem in detail.

The 'getUnique' function utilizes an object 'o' as a temporary storage for values. This works well for values that can serve as object keys, such as strings or numbers other than zero. However, JavaScript treats the number zero ('0') as a falsy value, which means 'o[0]' evaluates to 'false'.

When iterating over object keys, falsy values are skipped, resulting in the omission of zero from the resulting unique array. This behavior differs from the intended operation, which is to treat zero as a valid unique value.

Native Solution with Filter

In modern JavaScript environments (ES5 and above), a more concise and efficient approach is available using the 'filter' method:

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']

The 'filter' method takes a callback function that returns 'true' for each unique element to be included in the new array. In this case, our callback checks if the index of the current element in the array matches its position in the callback, confirming its uniqueness. This approach doesn't rely on object keys and handles zero values correctly.

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