Push from one array to another by reference

Question

Given this fiddle, does anyone have a suggestion as to how I might update the indices of array1? Or more to the point, any idea how to make the indices of array2 references to indices of array1?

http://jsfiddle.net/y8rs56r3/

    var array1 = [
        {num:"one"},
        {num:"two"},    
        {num:"three"}
    ];
    var array2 = [];
    var i = array1.length;
    while(i--){
        if(i!=1)array2.push(array1[i]);
    }

    array2[0].num = "one updated";
    console.log(array2);
    console.log(array1);

Obviously, in this codeblock, array1[0] is not updated.

What do you want to accomplish? By pushing as you have done, you have reversed the order of the elements (as well as excluded element i from array1). As it stands, array1[2] is the same object as array2[0] and is, in fact, updated in array1 as well as in array2. If you don't want to reverse, iterate in a forward direction. — Ted Hopp
– Ted Hopp, Commented Dec 17, 2014 at 17:36
@TedHopp, that's correct. array2 isn't just a clone of array1, or any given subset of consecutive indices of it. In the actual application, array2's indices can be anything from 0 to all of the indices of array1. — erfling
– erfling, Commented Dec 17, 2014 at 17:41
Well, that doesn't answer my main question: what do you want the behavior to be? — Ted Hopp
– Ted Hopp, Commented Dec 17, 2014 at 17:41
Your last statement is incorrect. Element array1[2] is updated, at least when I ran your fiddle. — Ted Hopp
– Ted Hopp, Commented Dec 17, 2014 at 18:04
Yep. As your loop is starting from the end the index 2 of the array1 is changed from {num:"three"} to {num:"one updated"}. — Sampath Liyanage
– Sampath Liyanage, Commented Dec 17, 2014 at 18:19

Suchit kumar · Accepted Answer · 2014-12-17 17:41:16Z

1

since your array is set of objects try like this:

  var array1 = [
              {num:"one"},
              {num:"two"},    
              {num:"three"}
          ];
       var array2 = [];
         for(x in array1){
                   array2.push(array1[x]);
                    }
          array2[0].num = "one updated";
          console.log(array2);//output  [Object { num="one updated"}, Object { num="two"}, Object { num="three"}]
          console.log(array1);// output  [Object { num="one updated"}, Object { num="two"}, Object { num="three"}]

answered Dec 17, 2014 at 17:41

Suchit kumar

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3 Comments

erfling Over a year ago

Interesting. Why does this work when the while loop doesn't? Also, if I'm using this a lot in the context of a large application, potentially looping over large collections, should I start to worry about performance of the for in loop?

Suchit kumar Over a year ago

if you will assign objects they will reflect the changes to their references also.there might be an easy way but this is what i come up with.wait for some time and see if some other posts are coming.

Suchit kumar Over a year ago

to answer why it did not work in while, since you never assigned the first element of array1 to array2.

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