I have an array with a specified length and I'm trying to populate it with values that are dependent on each index.
let arr = new Array(someLength)
arr.map((v, i) => i * 2)
From what I know, this isn't working because map
skips undefined values.
I have a few questions:
map
work on something like [undefined, undefined]
?Is there anyway to accomplish this using ES6 array methods?
I know I can use a standard for
loop, but was wondering if there's a nicer way to do it.
for (let i = 0; i < arr.length; i++) {
arr[i] = i * 2
}
I've found one method so far, it's not really clean though.
arr = arr.fill(undefined).map((foo, i) => i * 2)
- Why does
.map
work on something like[undefined, undefined]
?
Consider these two scenarios
let a1 = [];
a1.length = 2;
a1; // [undefined × 2]
// vs
let a2 = [undefined, undefined];
a2; // [undefined, undefined]
What would be the result of Object.keys
on each of these?
Object.keys(a1); // []
Object.keys(a2); // ["0", "1"]
So, we can see the difference between the two - one has initialised keys, the other doesn't
- Is there anyway to accomplish this using ES6 array methods?
You already pointed out .fill
, you could also use Array.from
Array.from({length: 5}, (itm, idx) => 2 * idx); // [0, 2, 4, 6, 8]
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