CODEWITHSUNDEEP
node.jsasynchronous
Yar
Yar

Reputation: 7457

Fill an array asynchronously

I have two arrays here, filling one of them with random numbers:

var arr1 = [1];
var arr2 = [];

function arr1Filler() {
    arr2 = arr1;
    setTimeout(function() {
        for (var i = 0; i < 3; i++) {
            arr1[i] = Math.floor(Math.random()*5);
        }
        console.log('array 1:');
        console.log(arr1);
        console.log('array 2:');
        console.log(arr2);
    }, 500);
}

setInterval(arr1Filler, 1000);

in this example, why these two arrays are always equal. In other words, why I am getting something like this:

array 1:   
[ 3, 0, 1 ]
array 2:   
[ 3, 0, 1 ]
array 1:   
[ 0, 2, 3 ]
array 2:   
[ 0, 2, 3 ]
array 1:   
[ 1, 2, 4 ]
array 2:   
[ 1, 2, 4 ]

instead of a result like this (the last value of array 2 is the new value of array 1):

array 1:
[ 1 ]
array 2:
[ 3, 0, 1 ]
array 1:
[ 3, 0, 1 ]
array 2:
[ 0, 2, 3 ]
array 1:   
[ 0, 2, 3 ]
array 2:   
[ 1, 2, 4 ]

What should I do to get the second result which I expect?

Upvotes: 1

Views: 195

Answers (1)

lyjackal
lyjackal

Reputation: 3984

They are the same because you set the arrays to the same object here: 

arr2 = arr1;

So when you add to arr1, arr2 is always identical. What you want is a copy of arr1. You can use slice to effectively make a copy of an array.

arr2 = arr1.slice();


var arr1 = [1];
var arr2 = [];

function arr1Filler() {
    arr2 = arr1.slice();
    setTimeout(function() {
        for (var i = 0; i < 3; i++) {
            arr1[i] = Math.floor(Math.random()*5);
        }
        console.log('array 1:');
        console.log(arr1);
        console.log('array 2:');
        console.log(arr2);
    }, 500);
}

setInterval(arr1Filler, 1000);

Upvotes: 2

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