# JavaScript: Find every element that exists in any of the two given arrays once

## JavaScript fundamental (ES6 Syntax): Exercise-27 with Solution

Write a JavaScript program to find every element in any of the two given arrays at once, using the provided comparator function.

• Create a new Set() with all values of a and values in b for which the comparator finds no matches in a, using Array.prototype.findIndex().

Sample Solution:

JavaScript Code:

``````//#Source https://bit.ly/2neWfJ2
// Define a function called `union_With` that computes the union of two arrays with a custom comparison function.
// It removes duplicates based on the comparison function provided.
const union_With = (a, b, comp) =>
Array.from(
new Set([
...a,
...b.filter(x => a.findIndex(y => comp(x, y)) === -1)
]));

// Example usage
console.log(union_With([1, 1.2, 1.5, 3, 0], [1.9, 3, 0, 3.9], (a, b) => Math.round(a) === Math.round(b)));
console.log(union_With([1, 2, 3, 4], [1, 2, 3, 4, 5], (a, b) => Math.round(a) === Math.round(b)));
```
```

Output:

```[1,1.2,1.5,3,0,3.9]
[1,2,3,4,5]
```

Flowchart:

Live Demo:

See the Pen javascript-basic-exercise-1-27 by w3resource (@w3resource) on CodePen.

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