add/remove elements in array-like object

Question

I have an array-like object:

[1:Array[10], 2: Array[2], 3: Array[2], 4: Array[2], 5: Array[3], 6: Array[1]]

Im trying to remove the first two elements, do some stuff, and then insert them again at the same place.

Here is what i do:

array = Array.prototype.splice.call(array, 0,2);

When logging array in firefox it show this:

Array [ <2 empty slots>, Array[1], Array[2], Array[3], Array[1] ]

Looks good to me,I removed the first two elements and the array now starts with 2 empty slots.

So now, what I hope to do is to add objects to these 2 empty slots.

For simplicity, lets remove to items from the array and then insert them again at the same place:

var twoFirstItems = Array.prototype.slice.call(array, 0,2);
array = Array.prototype.splice.call(array, 0,2);

Now,to re-insert twoFirstItems I would think that I could do:

array.unshift(twoFirstItems)

This does not work as expected, it inserts the array but it does not have a key as it had before its modifikation. I assume this has to do with unshift not working the same with an array-like object as with an array.

So how do you remove/insert elements to an array-like-object properly?

If i do the following:

  console.log(array);
  console.log(typeof array);

The result:

Array [ <1 empty slot>, Array[2], Array[2], Array[2], Array[3], Array[1] ]
object

what do you mean by array-like, when you work with an array? — Nina Scholz
– Nina Scholz, Commented Oct 2, 2016 at 14:55
Yes, it appears to be an ordinary array but when i do: console.log(typeof array) it logs 'object'. — user2915962
– user2915962, Commented Oct 2, 2016 at 14:56
And if you check if it's an array the correct way. what does it say -> console.log(Array.isArray(array) ) — adeneo
– adeneo, Commented Oct 2, 2016 at 15:01
typeof [] always returns object, all arrays are objects as well and typeof is not designed to distinguish different types of objects. — Álvaro González
– Álvaro González, Commented Oct 2, 2016 at 15:10

Pranesh Ravi · Accepted Answer · 2016-10-02 15:04:16Z

1

Without any complications, you can just re-assign the modified array at that index.

var a = [
  [1, 2, 3, 4, 5, 6],
  [1, 2, 3, 4, 5, 6],
  [1, 2, 3, 4, 5, 6],
  [1, 2, 3, 4, 5, 6]

]

a[0] = a[0].map((el) => el * 10)
a[1] = a[1].map((el) => el * 20)

console.log(a)

answered Oct 2, 2016 at 15:04

Pranesh Ravi

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