Sum all even numbers

1

This is taking me way longer than it should to work this out, can someone please help?

I was asked this in an interview yesterday and thought I’d get it down on paper so I can remember next time, well I can’t

The question was sum all even numbers in the array and also account for the null, I thought I could do this

arr = [2, 3, 4, 5, null, 6, 9]

arr.forEach(i => {
  if (i % 2 === 0) {
    i = i + i   
  } 
  console.log(i)
  return i
})

Then put it into it’s own variable functional programming style, like:

arr = [2, 3, 4, 5, null, 6, 9]

conat result = arr.forEach(i => {
  if (i % 2 === 0) {
    i = i + i   
  } 
  console.log(i)
  return i
})

console.log(result)

This has totally killed any confidence I had and I’m beginning to think my whole life is a lie :upside_down_face:

2 
arr = [2, 3, 4, 5, null, 6, 9] //Declare variables with `var`, `let`, or `const`
arr.forEach(i => {
  if (i % 2 === 0) {
    i = i + i //this doubles i; it doesn't sum it with other values
//in the array
  } 
  console.log(i) //unnecessary except for testing
  return i //forEach just executes some code for each item in the array
//the returned value is lost
})

You want to use something like .reduce() instead.

5

I actually realized that the "account for null" in the question isn’t usually going to make a difference, as null just coerces to 0.

const arr = [1,2,null,3,4];

function addEven(arr) {
  return arr.reduce((acc, cur) => cur % 2 === 0 ? acc + cur : acc, 0);
}

addEven(arr); // => 6

^ works just as well.

Edit: I also just realized you need to initialize these with 0, otherwise the first value of the array is used (even if odd).

1 Like
6

Thanks @lionel-rowe, there was so much wrong with it, I really need to practice more

Thanks

@Oxyrus and @jlave did you have anything to add?