How to get unique values in an array

Question

How can I get a list of unique values in an array? Do I always have to use a second array or is there something similar to java\'s hashmap in JavaScript?

I am going

Answer 1

Majority of the solutions above have a high run time complexity.

Here is the solution that uses reduce and can do the job in O(n) time.

Array.prototype.unique = Array.prototype.unique || function() {
        var arr = [];
	this.reduce(function (hash, num) {
		if(typeof hash[num] === 'undefined') {
			hash[num] = 1; 
			arr.push(num);
		}
		return hash;
	}, {});
	return arr;
}
    
var myArr = [3,1,2,3,3,3];
console.log(myArr.unique()); //[3,1,2];

Note:

This solution is not dependent on reduce. The idea is to create an object map and push unique ones into the array.