JavaScript: How to get the union of 2-3 sets without any library/package functions [duplicate]

Question

I'm just asking how to make a function that will return the union of sets !!but without any libraries and package functions. Maybe, only cycles and basic array methods. Thanks in advance for any useful reply))

For instance: I have an array a = [1, 2, 3, 4] and b = [3, 4, 5, 6].

How do I get c = [1, 2, 3, 4, 5, 6]

@N.Levenets, Given your comment at the first answer, please update your question so that you differentiate between your use of the word "set" and ES6 sets. And please show your effort. There is little appreciation for questions which show no research effort (hence the downvotes). Anyway, this question has been asked before, so better not waste more time on it. — trincot
– trincot, Commented Oct 16, 2018 at 18:36

Eugene Tsakh · Accepted Answer · 2018-10-16 18:39:30Z

If you mean ES6 sets then you can do it simply:

function union(...sets) { return new Set([].concat(...sets.map(set => [...set]))); }

Then union(new Set([1, 2, 3]), new Set([3, 4, 5])); will return Set(4) {1, 2, 3, 4, 5}

If you need it to be done with ES5:

function unique(arr) { var result = []; for (var i = 0; i < arr.length; i++) { if (result.indexOf(arr[i]) === -1) { result.push(arr[i]); } } return result; } function union() { var result = []; for (var i = 0; i < arguments.length; i++) { result = result.concat(arguments[i]); } return unique(result); }

And usage will be

union([1, 2, 3], [3, 4, 5], [4, 5, 6]); // => [1, 2, 3, 4, 5, 6]

Well, this is pretty good and reasonable, however I need it to be done without Set objects. Only arrays, strings and simple methods...
@Eugene_Tsakh That's pretty much what I wanted. Thanks a lot!

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