Changing a value in first object results in second object change

Question

I have an object array:

const test = new Array(2).fill({ a: 1, b: 2 });

test[0].a = 3;

I just want to reassign "a" in the first object, but when I use the above code, both "a" gets reassigned. And the output:

[ { a: 3, b: 2 }, { a: 3, b: 2 } ]

Answer 1

As stated in eg this documentation of the Array fill method

If the first parameter is an object, each slot in the array will reference that object.

A possible solution:

const test = Array.from({ length: 2 }).map(() => ({ a: 1, b: 2 }));

test[0].a = 3;

console.log(test);