How to initialize an array’s length in JavaScript?

Question

Array(5) gives you an array with length 5 but no values, hence you can’t iterate over it.
Array.apply(null, Array(5)).map(function () {}) gives you an array with length 5 and undefined as values, now it can be iterated over.
Array.apply(null, Array(5)).map(function (x, i) { return i; }) gives you an array with length 5 and values 0,1,2,3,4.
Array(5).forEach(alert) does nothing, Array.apply(null, Array(5)).forEach(alert) gives you 5 alerts
ES6 gives us Array.from so now you can also use Array.from(Array(5)).forEach(alert)
If you want to initialize with a certain value, these are good to knows…
Array.from('abcde'), Array.from('x'.repeat(5))
or Array.from({length: 5}, (v, i) => i) // gives [0, 1, 2, 3, 4]