JSFiddle - React, Tailwind, and code Playground

JavaScript

var arrayA = ['a','b','c','a'];
var arrayB = ['a','d','f','c'];

function non_duplicate(arr1, arr2) {
      diff = [];
      joined = arr1.concat(arr2);
      for( i = 0; i <= joined.length; i++ ) {
        current = joined[i];
        if( joined.indexOf(current) == joined.lastIndexOf(current) ) {
          diff.push(current);
        }
      }
      return diff;
    }


var union = non_duplicate(arrayA,arrayB );
alert(union);