Declare an empty two-dimensional array in Javascript?

Question

I want to create a two dimensional array in Javascript where I'm going to store coordinates (x,y). I don't know yet how many pairs of coordinates I will have because they will be dynamically generated by user input.

Example of pre-defined 2d array:

var Arr=[[1,2],[3,4],[5,6]]; 

I guess I can use the PUSH method to add a new record at the end of the array.

How do I declare an empty two dimensional array so that when I use my first Arr.push() it will be added to the index 0, and every next record written by push will take the next index?

This is probably very easy to do, I'm just a newbie with JS, and I would appreciate if someone could write a short working code snippet that I could examine. Thanks

Answer 1

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 ] 

Answer 2

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.