Array.prototype.fill({}) references

Question

Can somebody explain please how this code works under the hood:

let arr = Array(3).fill({}) // [{}, {}, {}]
arr[0].hi = "hi"            // [{ hi: "hi" }, { hi: "hi" }, { hi: "hi" }]

Why does this reference all elements? And how would I reference only the first one?

You can reference the first element without referencing the rest of the elements by copying it's value, setting the value to something else and reinserting it like this: `let f = arr[0]; f={hi: "hi"}; arr[0] = first;` — apena, Jun 18 '20 at 23:56

score 2 · Accepted Answer · answered Jun 18 '20 at 23:46

2

You are filling each position in the array with the same reference of an object, it is the same as

let a = {};
const b = a;
a.hi = 'hi';
console.log(b);

answered Jun 18 '20 at 23:46

Adrian Brand

1 Answers1