6

so, I have a 2d array, which i decalre like this: 

var grille = new Array(60).fill(new Array(30).fill(false));

I want to be able to change the value of one cell in the array, but when i do

grille[x][y] = "new value";

I have all the x array which contains "new value" at the index y, instead of array[x][y].

so i have

grille[1][y] = "new value"
grille[2][y] = "new value"
grille[3][y] = "new value"

instead of

grille[x][y] = "new value"
grille[1][y] = false

for example. It may be a noob error, but i'm very new to javascript and don't know how to do this.

Thanks for your help.

Joël
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  • Not clear what the problem/question is. – Waxi Mar 08 '17 at 14:09
  • I want to do `grille[x][y] = "new value"` , to change the value of `grille[x][y]`, but when i do this, not only `grille[x][y]` is changed, but also `grille[1][y], grille[2][y],...` and i don't know why – Joël Mar 08 '17 at 14:25
  • Not the best person to explain this, but the issue is that all the arrays in grille are not actually unique, they are all sharing the same referenced array, which happens when you create them the way you did. I think you're looking for a 'deep copy' of the array. – Waxi Mar 08 '17 at 14:36

3 Answers3

8

In your case 'new Array(30).fill(false)' will be created only once. It wont be created for each element in 'new Array(60)'. So all 60 cells holds the same array reference. So, if you change one - it will update all its reference.

var grille = (new Array(60)).fill().map(function(){ return new Array(30).fill(false);});

Here, for each element in 'new Array(60)' 'new Array(30)' will be created and each cell hold a different reference now. Hope this helps.

ajai Jothi
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1

So what I was doing with this is that var grille = new Array(60).fill(new Array(30).fill(false)); filled grille with the same new array(30) and it wasn't creating a new array for each index of grille like I thought. So What I did instead is this 

grille= new Array(60);
for (var i = 0; i < grille.length; i++) {
    grille[i] = new Array(30).fill(false);
}
Joël
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0

Anyways, since the ES5 (I believe), you can do it this way:

var grille = Array.from(new Array(60),_=>new Array(30).fill(false))
Mexolius
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