# What is the importance of _.union() method in JavaScript?

JavascriptObject Oriented ProgrammingFront End Technology

## _.union()

_.Union() method belongs to underscore.js a library of javascript. The _.union() function is used to take n number of arrays and return a new array with the unique terms in all those arrays (union of all array). It scrutinizes each and every value of the arrays and pushes out unique values into another array.

### syntax

_.union( array1, array2, .... );

### Example

In the following example, _.union() is used to get an array of unique elements.

Live Demo

<html>
<body>
<script
src ="https://cdnjs.cloudflare.com/ajax/libs/underscore.js/1.9.1/underscore-min.js" >
</script>
<body>
<script type="text/javascript">
document.write(_.union([1, 2, 9, 40],
[1, 20, 3, 2],
[9, 2]));
</script>
</body>
</html>

### Output

1,2,9,40,20,3

The arrays can consist of not only numbers or strings but also empty strings or falsy values.

### Example

In the following example, all kinds of values are used in arrays. Even though, _.union() has done its task of giving a new array with unique values.

Live Demo

<html>
<body>
<script
src ="https://cdnjs.cloudflare.com/ajax/libs/underscore.js/1.9.1/underscore-min.js" >
</script>
<body>
<script type="text/javascript">
document.write(_.union(["hello",2, "hi", 1, ""],
['the', undefined],
['', null],
["*", ""]));
</script>
</body>
</html>

### Output

hello,2,hi,1,,the,,,*
Published on 10-Jul-2019 15:18:52