Getting a union of two arrays in JavaScript [duplicate]

Question

Say I have an array of [34, 35, 45, 48, 49] and another array of [48, 55]. How can I get a resulting array of [34, 35, 45, 48, 49, 55]?

Answer 1

With the arrival of ES6 with sets and splat operator (at the time of being works only in Firefox, check compatibility table), you can write the following cryptic one liner:

var a = [34, 35, 45, 48, 49];  var b = [48, 55];  var union = [...new Set([...a, ...b])];  console.log(union);

Little explanation about this line: [...a, ...b] concatenates two arrays, you can use a.concat(b) as well. new Set() create a set out of it and thus your union. And the last [...x] converts it back to an array.

Answer 2

If you don't need to keep the order, and consider 45 and "45" to be the same:

function union_arrays (x, y) {    var obj = {};    for (var i = x.length-1; i >= 0; -- i)       obj[x[i]] = x[i];    for (var i = y.length-1; i >= 0; -- i)       obj[y[i]] = y[i];    var res = []    for (var k in obj) {      if (obj.hasOwnProperty(k))  // <-- optional        res.push(obj[k]);    }    return res;  }    console.log(union_arrays([34,35,45,48,49], [44,55]));