CODEWITHSUNDEEP
javascriptarrays
g97
g97

Reputation: 35

Pushing an array to another array

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.

Upvotes: 1

Views: 182

Answers (2)

Unmitigated
Unmitigated

Reputation: 89139

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));

Upvotes: 1

ad007
ad007

Reputation: 146

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)

Upvotes: 1

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