How to get index of an empty element of an array?

I have a JavaScript array with some empty (maybe null or undefined) elements. I need to find those empty indexes (1 and 3).

['red',,'orange',,'blue','white','black']

But my solution is not working:

for (let i = 0; i < array.length; i++) {
    if (array[i] === undefined) { // Same problem with null or ''
        console.log('No color: ' + i);
    }
}

Snippet:

const array = ['red', , 'orange', , 'blue', 'white', 'black'];

for (let i = 0; i < array.length; i++) {
  if (array[i] === undefined) { // Same problem with null or ''
    console.log('No color: ' + i);
  }
}

Answer

Use a blank string to compare to get the answer you desire. If you also want to check for undefined you can use logical or to check both of them.

const array = ['red','',  'orange',,  'blue', 'white', 'black'];

for (let i = 0; i < array.length; i++) {
  if (array[i] === '' || array[i] === undefined) { 
console.log('No color: ' + i);
}
}