Array.concat() or the spread syntax creates shallow copies.

createShallowCopy.js

const original = [
  [0, 0, 0, 0, 0, 0, 0],
  [0, 0, 0, 0, 0, 0, 0],
  [0, 0, 0, 0, 0, 0, 0]
];

const clone = [...original];

console.log(original === clone); // false.
console.log(original[0] === clone[0]); // true.

original.splice(0, 2); // clone would not be altered.

original[0].splice(0, 2, 'a'); // clone _will_ be altered because sub-arrays are passed in as reference.

// Same scenario with Array.concat().