javascript - How do you assign a value inside a forEach loop?

I expected the first console.log to be [0,10,20,30] and the second to be [0,100,20,30]:

var arr = [0,10,20,30]
console.log(arr)

arr.forEach(each)
console.log(arr)

function each(data,index) {
   if (index === 1) {
      data = 100 // This isn't assigned to arr[1]
   }
}