how to make elements in an array represent each other code example

Example 1: javascript get intersection of two arrays

function getArraysIntersection(a1,a2){
    return  a1.filter(function(n) { return a2.indexOf(n) !== -1;});
}
var colors1 = ["red","blue","green"];
var colors2 = ["red","yellow","blue"];
var intersectingColors=getArraysIntersection(colors1, colors2); //["red", "blue"]

Example 2: how to put two items befside each other using flexbox

<div class="flex-column">
  <div class="column-item">a</div>
  <div class="column-item">b</div>
  <div class="column-item">c</div>
  <div class="column-item">d</div>
  <div class="column-item">e</div>
</div>