.join(','), code example
Example 1: join in array
var a = ['Wind', 'Water', 'Fire'];
a.join(); // 'Wind,Water,Fire'
a.join(', '); // 'Wind, Water, Fire'
a.join(' + '); // 'Wind + Water + Fire'
a.join(''); // 'WindWaterFire'
Example 2: join array javascript
<html>
<select multiple class="select-colors">
<option>blue</option>
<option>green</option>
</select>
</html>
<script>
var myColorSelect = $(".select-colors").val().join();
console.log(myColorSelect);
</script>