I've observed this in Firefox-3.5.7/Firebug-1.5.3 and Firefox-3.6.16/Firebug-1.6.2
When I fire up Firebug:
What's going on here? Is this a bug, or am I misunderstanding how to use new Array(3)
?
I had a task that I only knew the length of the array and needed to transform the items. I wanted to do something like this:
let arr = new Array(10).map((val,idx) => idx);
To quickly create an array like this:
[0,1,2,3,4,5,6,7,8,9]
But it didn't work because: (see Jonathan Lonowski's answer a few answers above)
The solution could be to fill up the array items with any value (even with undefined) using Array.prototype.fill()
let arr = new Array(10).fill(undefined).map((val,idx) => idx);
console.log(new Array(10).fill(undefined).map((val, idx) => idx));
Update
Another solution could be:
let arr = Array.apply(null, Array(10)).map((val, idx) => idx);
console.log(Array.apply(null, Array(10)).map((val, idx) => idx));