javascript creating multi-dimensional array syntax

Question

Today I've heard that it's possible to create a multi - dimensional array in js using this syntax:

var a = new Array(3,3);
a[2][2] = 2;
alert(a[2][2])

However this doesn't work in opera. Am I wrong somewhere?

This is one of the reasons why **not** to use `new Array()`. If you pass only one argument, you indeed set the length of the array to that argument. But if you pass more than one, it generates an array containing those elements. There is no need to use `Array()`, use literal notation instead `[]`. — Felix Kling, Feb 10 '11 at 20:28

score 7 · Accepted Answer · answered Feb 10 '11 at 20:13

Yes, you are wrong somewhere. var a = new Array(3,3); means the same as var a = [3,3];. It creates an array with two members: the Number 3 and the Number 3 again.

The array constructor is one of the worst parts of the JavaScript language design. Given a single value, it determines the length of the array. Given multiple values, it uses them to initialise the array.

Always use the var a = []; syntax. It is consistent (as well as being shorter and easier to read).

There is no short-cut syntax for creating an array of arrays. You have to construct each one separately.

var a = [ 
          [1,2,3],
          [4,5,6],
          [7,8,9]
         ];

I believe OP was trying to create a multi-dimensional Array with that syntax. EDIT: *This comment is no longer relevant.* — user113716, Feb 10 '11 at 20:16
You are right. I was told it creates a multi-dim array. Thanks for good and clear answer — Dan, Feb 10 '11 at 20:20

Chris Baker · Answer 2 · 2014-10-15T18:41:54.373

2

The code you posted makes an array consisting of two integers. You're then trying to treat an integer as an array.

mv = new Array();
mv[0] = new Array();
mv[0][0] = "value1-1";
mv[0][1] = "value1-2";

mv[1] = new Array();
mv[1][0] = "value2-1";
mv[1][1] = "value2-2";

There is no way to directly instantiate a multidimensional array.

edited Oct 15 '14 at 18:41

answered Feb 10 '11 at 20:14

Chris Baker

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In the second block, don't you mean `mv[1][0]` and `mv[1][1]`? – jlewkovich Oct 15 '14 at 17:22
The only script that solved it for me with 3 dimentions... Thx. – JanBorup Aug 26 '15 at 13:55

score 0 · Answer 3 · answered Feb 10 '11 at 20:18

you want to create an array of arrays, but you're creating an array with 2 elements:

var a = new Array(3,3);
// a = [3,3]

if you want to create a multidimensional array, you have to think in terms of array of arrays.
this way, a 2 dimensional array (or matrix) would be defined as :

var a = [[],[]];//or var a = new Array([],[]);
//or if you want to initialize the matrix : 
var b = [
    [1,2],
    [3,4]
];

javascript creating multi-dimensional array syntax

3 Answers3

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