Array.prototype.unique1 = function() {
var arr = [];
for (var i = 0; i < this.length; i++) {
var item = this[i];
if (arr.indexOf(item) === -1) {
arr.push(item);
}
}
return arr;
}
[1,2,3,'4',3,4,3,1,'34',2].unique1(); //[1, 2, 3, "4", 4, "34"]

var indexOf = [].indexOf ? function(arr, item) {
return arr.indexOf(item);
} :
function indexOf(arr, item) {
for (var i = 0; i < arr.length; i++) {
if (arr[i] === item) {
return i;
}
}
return -1;
}
Array.prototype.unique2 = function() {
var arr = [];
for (var i = 0; i < this.length; i++) {
var item = this[i];
if (arr.indexOf(item) === -1) {
arr.push(item);
}
}
return arr;
}
[1,2,3,'4',3,4,3,1,'34',2].unique2(); //[1, 2, 3, "4", 4, "34"]

Array.prototype.unique3 = function(){
var arr = [this[0]]; 
for(var i = 1; i < this.length; i++) 
{
if (this.indexOf(this[i]) == i){
arr.push(this[i]);
} 
}
return arr;
}
[1,2,3,'4',3,4,3,1,'34',2].unique3(); //[1, 2, 3, "4", 4, "34"]

Array.prototype.unique4 = function() {
var arr = [];
var hash = {};
for (var i = 0; i < this.length; i++) {
var item = this[i];
var key = typeof(item) + item
if (hash[key] !== 1) {
arr.push(item);
hash[key] = 1;
}
} 
return arr;
}
[1,2,3,'4',3,4,3,1,'34',2].unique4(); //[1, 2, 3, "4", 4, "34"]

Array.prototype.unique5 = function(){
var arr=[];
var hash={};
for(var i=0,len=this.length;i<len;i++){
if(!hash[this[i]]){ 
arr.push(this[i]);
hash[this[i]]=true;
}
}
return arr;
}
[1,2,3,'4',3,4,3,1,'34',2].unique5(); //[1, 2, 3, "4", "34"]

Array.prototype.unique6 = function(){
this.sort();
var arr = [this[0]];
for(var i = 1; i < this.length; i++){
if( this[i] !== arr[arr.length-1]){
arr.push(this[i]);
}
}
return arr;
}
[1,2,3,'4',3,4,3,1,'34',2].unique6(); //[1, 2, 3, "34", "4", 4]

function compare(value1,value2) {
if (value1 < value2) {
return -1;
} else if (value1 > value2) {
return 1;
} else {
return 0;
}
}
[1,2,5,2,10,3,20].sort(compare); //[1, 2, 2, 3, 5, 10, 20]

Array.prototype.unique7 = function(){
return Array.from(new Set(this));
}
[1,2,3,'4',3,4,3,1,'34',2].unique7(); //[1, 2, 3, "4", 4, "34"]

const _ = require('underscore');
_.uniq([1, 2, 1, 3, 1, 4]); //[1, 2, 3, 4]

console.time("test");
[1,2,3,'4',3,4,3,1,'34',2].unique7();
console.timeEnd("test");
==> VM314:3 test: 0.378ms

var arr = [];
var num = 0;
for(var i = 0; i < 1000000; i++){
num = Math.floor(Math.random()*100);
arr.push(num);
}
console.time("test");
arr.unique7();
console.timeEnd("test");