How to copy an array of JSON objects in javascript

Question

I have an array of objects in JavaScript. e.g. current_films[0].f_name, current_films[0].f_pattern etc. I want to copy the array into another similiar to the following:

for(var i=0; i<current_films.length; i++)
    {
            if(current_films[i].f_material == Value)
                {
                    temp[i] = current_films[i];
                }
    }

However, there seems to be an inexplicable problem when I do this. By inexplicable problem, I mean that the code does not execute and the array is not copied as I desire.

Any help would be greatly appreciated. Thank you!

P.S. Could you please mention why the above code would not work? As in, if I put an alert("Reached here");, it's not getting executed. Any ideas why its so?

What is Value? Can you give us a sample data that you expect to get? — Ionică Bizău
– Ionică Bizău, Commented Oct 12, 2013 at 16:26
Your temp array will be sparse -- the indexes will not be sequential from 0, only the indexes from current_film that match Value will exist. Is that the problem? — Barmar
– Barmar, Commented Oct 12, 2013 at 16:30
Value is just a string. Right now, I am just trying to copy all those objects whose f_material attribute matches Value — Saket Jain
– Saket Jain, Commented Oct 12, 2013 at 16:31

nkron · Accepted Answer · 2013-10-12 16:55:15Z

2

One problem I see is that you set temp[i] to the value which means there would be gaps in the temp array. You could use push() to append the value to temp so you don't need to manage two sets of indices.

You could also use JavaScript's Array.filter() to do this a little easier. Filter will return a new array of the values from the original array where your function returns true.

var temp = current_films.filter(function(film) {
  return (film.f_material === Value);
});

edited Oct 12, 2013 at 16:55

answered Oct 12, 2013 at 16:32

nkron

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4 Comments

Mohit Over a year ago

consider cloning if required.

Sriharsha Over a year ago

@nkron I would use === instead of ==

nkron Over a year ago

Yeah, that would be better. I've made that change.

Saket Jain Over a year ago

Thanks @nkron! This worked! Do you have any idea why the code I wrote was not allowing an alert("Reached here"); to execute?

Paolo · Accepted Answer · 2013-10-12 17:09:24Z

P.S. Could you please mention why the above code would not work? As in, if I put an alert("Reached here");, it's not getting executed. Any ideas why its so?

I'd guess f_material is not defined for every element in the array.

If that's the case I'd use

if(typeof(current_films[i].f_material)!=='undefined')
{
    if(current_films[i].f_material == Value)
    {
        temp[i] = current_films[i];
    }
}

Anyway I'd suggest you to get familiar with the browser's javascript debugger (assumed that code runs in a browser)

Finally note that you're not copying the array/object:

temp[i] is a reference to current_films[i]

Modifying current_films later in the code will result in modifying temp

If that's not the behaviour desired Google for "javascript object copy".

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