how to write a program that prints the largest value that occurs simultaneously in both arrays?

I have to create two 10-elements arrays with random values from 1 to 20 and write a program that prints the largest value that occurs simultaneously in both arrays.

I created two tabs like below. The program should prints the largest value that occurs simultaneously in both arrays. Here it should be 11. I know just how to catch the max value from the array. I appreciate help.

<script>
var max = 0;
var tab = [1, 2, 5, 8, 9, 11, 15, 16, 17, 20];
var tab2 = [3, 4, 6, 7, 10, 11, 12, 13, 14, 18];
for (var i = 0; i < tab.length; i++) {
if (max <= tab[i]) {
max = tab[i];
}
}
console.log(max);
</script>

to find the largest value use nested loops to compare each element of both arrays as follow

<!-- begin snippet: js hide: false console: true babel: false -->

<!-- language: lang-js -->

var tab = [1, 2, 5, 8, 9, 11, 15, 16, 17, 20];
var tab2 = [3, 4, 6, 7, 10, 11, 12, 13, 14, 18];
var max = 0;
for (var i = 0; i < tab.length; i++) {
  for (var j = 0; j < tab2.length; j++) {
    if (tab[i] === tab2[j] && tab[i] > max) {
      max = tab[i];
    }
  }
}
console.log(max);

<!-- end snippet -->

I'd do this:

<!-- begin snippet: js hide: false console: true babel: false -->

<!-- language: lang-js -->

// const {intersection,max} require('lodash/fp'}
const { intersection, max } = _;

const tab = [1, 2, 5, 8, 9, 11, 15, 16, 17, 20];
const tab2 = [3, 4, 6, 7, 10, 11, 12, 13, 14, 18];

const res = max(intersection(tab, tab2))

console.log({
  intersection: intersection(tab, tab2),
  max: max(intersection(tab, tab2)),
});

<!-- language: lang-html -->

<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.17.21/lodash.min.js"></script>

<!-- end snippet -->

You can translate that into straight javascript, especially if it's for a homework assignment :).

The approach is as follows ...

• get the intersection of both arrays

• get the maximum value of the just computed intersection

... which then boils down either to coming up with an own implementation of an intersection functionality or to making use of a third party library / helper functionality.

The below example code features one possible implementation of getIntersection which makes use of ...

• Array.from in order to always ensure the processing of array parameters,

• Array.prototype.sort in order to help optimally assign the participating arrays for the best computation performance,

• Array.prototype.reduce and a Map instance for creating a lookup-table in order to achieve a more performant filter process when it comes to the actual computation of the intersection,

• Array.prototype.filter and Map.prototype.has for finally computing the intersection result.

<!-- begin snippet: js hide: false console: true babel: false -->

<!-- language: lang-js -->

function getIntersection(firstIterable = [], secondIterable = []) {
  const [

    comparisonBase, // ... compare to the shorter array.
    comparisonList, // ... filter from the longer array.

  ] = [Array.from(firstIterable), Array.from(secondIterable)]
    // - ensure two arrays (line above)
    // - and sort them according to each array's `length`.
    .sort((a, b) => a.length - b.length);

  // create a `Set` based lookup from the shorter array.
  const itemLookup = new Set(comparisonBase);

  // the intersection is the result of following filter task.
  return comparisonList.filter(item => itemLookup.has(item));
}

const tab = [1, 2, 4, 5, 8, 9, 11, 15, 16, 17, 20, 21, 0];
const tab2 = [3, 4, 6, 7, 9, 10, 11, 12, 13, 14, 18, 19, 0];

console.log(
  'intersection of `tab` and `tab2` ...',
  getIntersection(tab, tab2)
);
console.log(
  'max value of the intersection of `tab` and `tab2` ...',
  Math.max(...getIntersection(tab, tab2))
);

<!-- end snippet -->