Typescript/Javascript array push pushes to all arrays in 2d array

Question

This should be very basic but do not working. I am trying to push an element on 2d number array on a specific index, but it is inserting element on every index.

 let adj = new Array(4).fill(new Array()) adj[0].push(1) console.log(adj)

The output I am getting:

[[1], [1], [1], [1]] 

But I am expecting:

[[1], [], [], []]

Answer 1

What you're doing with let adj = new Array(4).fill(new Array()) is just setting adj to an array of references to the same array, thus changing one, changes the others.

To fix this do it like this

 let adj = Array.from(Array(4), () => new Array()); adj[0].push(1); console.log(adj)