Why the confusion in arrays?

Question

JavaScript

let newArray = [];
let row = [];
for (let i = 0; i < 3; i++) {
    for (let j = 0; j < 2; j++) {
      row.push(0);
    }
    console.log(row)//видим, что сначала 2 элемента, потом 4, потом 6
    newArray.push(row);
  }
console.log(newArray);

It turns
out [ [ 0, 0, 0, 0, 0, 0 ],
[ 0, 0, 0, 0, 0, 0 ],
[ 0, 0, 0, 0, 0, 0 ] ]

and not


Why?

Answer 1

Because the row array is passed by reference to the newArray array, that is, each time you write newArray.push(row), you do not fix the current state of row in newArray, but make a reference to the same row variable, which you change later .
To test this thesis, you can run, for example, the following code:

let a = [1, 2];
let b = [a, a];
console.log(b); // 
a.push(3); // теперь изменим a и окажется
console.log(b); // 

If you want the newArray keys to have three different states of the row array, use the slice function for example:

let newArray = [];
let row = [];
for (let i = 0; i < 3; i++) {
    for (let j = 0; j < 2; j++) {
      row.push(0);
    }
    console.log(row)//видим, что сначала 2 элемента, потом 4, потом 6
    newArray.push(row.slice()); // функция slice() без аргументов возвращает копию массива, на котором применена
  }
console.log(newArray);