var a = ["CS348", "CS353", "CS381", "CS422", "CS448", "CS490-ES0", "CS490-DSO"];

var b = ["CS348", "CS352", "CS353", "CS354", "CS381", "CS422", "CS448", "CS456", "CS473", "CS490-DSO", "CS490-ES0"];

​

​

​

var output = [];

​

​

console.log('----before code-----');

console.log(a, b, output);

​

​

for (var i = 0; i < a.length; i++) {

  var indexInB = b.indexOf(a[i]);

  if (indexInB > -1){

    output.push(a[i]);

    a.splice(i, 1);

    b.splice(indexInB, 1);

    i--;

  }

}

console.log('----after code-----');

console.log(a, b, output);

​

​

​

​

​

​

​

​

​