Declare an empty two-dimensional array in Javascript?

If you want to initialize along with the creation, you can use fill and map.

const matrix = new Array(5).fill(0).map(() => new Array(4).fill(0));

5 is the number of rows and 4 is the number of columns.

ES6

Matrix m with size 3 rows and 5 columns (remove .fill(0) to not init by zero)

[...Array(3)].map(_=>Array(5).fill(0))       

let Array2D = (r,c) => [...Array(r)].map(_=>Array(c).fill(0));

let m = Array2D(3,5);

m[1][0] = 2;  // second row, first column
m[2][4] = 8;  // last row, last column

// print formated array
console.log(JSON.stringify(m)
  .replace(/(\[\[)(.*)(\]\])/g,'[\n  [$2]\n]').replace(/],/g,'],\n  ')
);

You can just declare a regular array like so:

var arry = [];

Then when you have a pair of values to add to the array, all you need to do is:

arry.push([value_1, value2]);

And yes, the first time you call arry.push, the pair of values will be placed at index 0.

From the nodejs repl:

> var arry = [];
undefined
> arry.push([1,2]);
1
> arry
[ [ 1, 2 ] ]
> arry.push([2,3]);
2
> arry
[ [ 1, 2 ], [ 2, 3 ] ]

Of course, since javascript is dynamically typed, there will be no type checker enforcing that the array remains 2 dimensional. You will have to make sure to only add pairs of coordinates and not do the following:

> arry.push(100);
3
> arry
[ [ 1, 2 ],
  [ 2, 3 ],
  100 ]