I love JavaScript, however very often, it doesn’t love me back. const dataBuffers = new Array(4); dataBuffers.fill([]); for (let i = 0; i < 4; i += 1) { dataBuffers[i].push(7); } console.log(JSON.stringify(dataBuffers)); // guess what is the answer? If you guess the answer would be [[7],[7],[7],[7]], then think again. The problem is that dataBuffers.fill([]) will create you a single array, and fills the dataBuffers with the reference of the array. It is actually pretty clear if you have done JavaScript or any language long enough, but one might be stuck with the impression that the dataBuffers is filled with an empty array.