Pushing an array to another array-CodePudding

I'm new to javascript and I've been going through some exercises but I can't figure out why this code works like this,

    let newArray = [];
    let arr1 = [];
    for (let i = 0; i < 2; i  ) {

      for (let j = 0; j < 2; j  ) {

        arr1.push(0);
        //console.log('Arr1:',arr1); 
      }

      newArray.push(arr1);
      //console.log('New Array:', newArray)
      
    }
    console.log(newArray);

According to me, this block of code should output [[0,0][0,0,0,0]] but the real output is [[0,0,0,0][0,0,0,0]].

I tried console logging after every iteration(by removing the comments) and I can't seem to find where it goes wrong. It seems like it all goes well until the last log. I'd appreciate your help.

CodePudding user response：

One way to do it is to avoid using push() function and use concat() function instead. More about it on existing discussion.

You would have something like:

newArray = newArray.concat(arr)

CodePudding user response：

You should use Array#slice or spread syntax to copy the array instead of pushing the same reference multiple times, since subsequent changes will continue to be reflected.

let newArray = [];
let arr1 = [];
for (let i = 0; i < 2; i  ) {
  for (let j = 0; j < 2; j  ) {
    arr1.push(0);
  }
  newArray.push(arr1.slice());
}
console.log(JSON.stringify(newArray));