Page 116 - JavaScript

From ES5.1 onwards, you can use the native method Array.prototype.filter to loop through an
array and leave only entries that pass a given callback function.

In the following example, our callback checks if the given value occurs in the array. If it does, it is a
duplicate and will not be copied to the resulting array.

5.1

var uniqueArray = ['a', 1, 'a', 2, '1', 1].filter(function(value, index, self) {
return self.indexOf(value) === index;
}); // returns ['a', 1, 2, '1']

If your environment supports ES6, you can also use the Set object. This object lets you store
unique values of any type, whether primitive values or object references:

6

var uniqueArray = [... new Set(['a', 1, 'a', 2, '1', 1])];

See also the following anwsers on SO:

• Related SO answer
• Related answer with ES6

Removing all elements

var arr = [1, 2, 3, 4];

Method 1

Creates a new array and overwrites the existing array reference with a new one.

arr = [];

Care must be taken as this does not remove any items from the original array. The array may
have been closed over when passed to a function. The array will remain in memory for the life of
the function though you may not be aware of this. This is a common source of memory leaks.

Example of a memory leak resulting from bad array clearing:

var count = 0;

function addListener(arr) { // arr is closed over
var b = document.body.querySelector("#foo" + (count++));
b.addEventListener("click", function(e) { // this functions reference keeps
// the closure current while the
// event is active
// do something but does not need arr
});
}

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