JS: How to merge two arrays in Javascript and de-duplicate items

unique_merge.js

Array.prototype.unique = function() {
    var a = this.concat();
    for(var i=0; i<a.length; ++i) {
        for(var j=i+1; j<a.length; ++j) {
            if(a[i] === a[j])
                a.splice(j, 1);
        }
    }
    return a;
};

var array1 = [45,46,47,48,49,50,51,52,53,60,123,240,153,284,79,196,61,57, 268,111,129,152,78,342,345,89,110,120,270,350,
235,229,242,96,437,236,435,333,487,647,119,397,1018,882,1024,474,237,993,1167,376,380,622,
384,1010,1421,1186,1437,790,1644,874,2086,2118,2160,1684,1685,1683,2040,2349,2365,2366,
2417,2670,1029,3055,3044,3048,3046,3067,3071,3056,3058,1615,2781,2740,2794,2777,2749,2753,
2710,2691,1413,2793,2706,2758,1179,3607,3612,3619,3616,3617,
3610,3621,3613,3622,698,726];

var array2 = [45,46,47,49,50,51,51,53,59,60,83,107,122,123,388,395,339,57, 118,129,51,79,336,340,430,333,116,96,251,398,
626,268,332,103,504,229,534,382,408,410,563,378,78,461,424,665,555,463,606,474,406,726,706,462,464,480,673,
536,675,123,557,770,235,828,650,610,861,865,871,870,656,457,487,742,760,927,775,570,883,403,772,1011,819,1064,879,
878,1122,1120,1129,249,376,153,643,1027,647,1073,1114,1115,452,384,334,880,1169,995,785,1014,996,1365,1424,1669,
1646,1674,1332,1025,1026,864,1056,2260,1057,646,2384,1206,50,2398,1353,1177,2793,2405,2984,3026,3019,2990,1188,1146,1189];

var array3 = array1.concat(array2).unique();
alert(array3);