JavaScript Return an array that contains all the strings appearing in all the subarrays

We have an array of arrays like this −

const arr = [
   ['foo', 'bar', 'hey', 'oi'],
   ['foo', 'bar', 'hey'],
   ['foo', 'bar', 'anything'],
   ['bar', 'anything']
]

We are required to write a JavaScript function that takes in such array and returns an array that contains all the strings which appears in all the subarrays.

Let's write the code for this function

Example

const arr = [
   ['foo', 'bar', 'hey', 'oi'],
   ['foo', 'bar', 'hey'],
   ['foo', 'bar', 'anything'],
   ['bar', 'anything']
]
const commonArray = arr => {
   return arr.reduce((acc, val, index) => {
      return acc.filter(el => val.indexOf(el) !== -1);
   });
};
console.log(commonArray(arr));

Output

The output in the console will be −

['bar']