Javascript splice method remove values from two arrays

Question

Javascript (using jQuery):

var paragraphs = [
    ['This is my first paragraph content of the first array', 'This is my second paragraph content of the first array', 'This is my third paragraph content of the first array'],
    ['This is my first paragraph content of the second array', 'This is my second paragraph content of the second array', 'This is my third paragraph content of the second array']
],
text_box_value,
unused_paragraphs = null;

$(document).ready(function(){
    $('input#text_box').keyup(function(){
        text_box_value = $(this).val(); 
    });

    $('input#submit_button').click(function(){
        if(unused_paragraphs === null) {
            unused_paragraphs = paragraphs; 
        }

        for(var i = 0; i < unused_paragraphs.length; i++) {
            if(unused_paragraphs[i].length == 0)
                unused_paragraphs[i] = paragraphs[i];

            while(unused_paragraphs[i].length != 0) {
                var rand = Math.floor(Math.random() * unused_paragraphs[i].length);
                if(unused_paragraphs[i][rand].search(text_box_value) !== -1) {
                    $("#paragraphs_container").append('<p>' + unused_paragraphs[i][rand] + '</p>');
                    break;
                }

                unused_paragraphs[i].splice(rand, 1);
            }   
        }

        console.log(unused_paragraphs);
        console.log(paragraphs);

    });

});

My question is why when I use splice method on unused_paragraphs variable it also remove the value from the paragraphs variable

Later edit JSFiddle

Sounds like you only have one array but two variables referencing it. — Bergi
– Bergi, Commented Dec 17, 2012 at 11:04

Luca Rainone · Accepted Answer · 2012-12-17 11:03:16Z

1

javascript objects/array are stored by reference.

If you want a copy that's a trick:

if(typeof unused_paragraphs == "undefined") {
        var unused_paragraphs = [];
        for(var i = 0; i<paragraphs.length; i++) {
            unused_paragraphs[i] = paragraphs[i].slice(0);  
        }
}

and

unused_paragraphs[i] = paragraphs[i].slice(0);

edited Dec 17, 2012 at 11:03

answered Dec 17, 2012 at 10:28

Luca Rainone

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4 Comments

Mihai Matei Over a year ago

I've tried this but now the problem is that splice method is not working anymore.. The found value is not removed from the array.. Why's that?

I.G. Pascual Over a year ago

This solution works for me @MateiMihai, did you change both lines? which version of jQuery are you using?

Luca Rainone Over a year ago

For an advanced copy function, you can see also this answer (stackoverflow.com/questions/2294703/…).

Mihai Matei Over a year ago

Thank you for your answer, it was what I've expected but I have to review my code because now there is something else which is not working. Thank you

bipen · Accepted Answer · 2012-12-17 10:49:04Z

1

to copy the obect to new object..

try this..

var unused_paragraphs= jQuery.extend(true, {}, paragraphs);

here is just an example of copied objects.. check it out

http://jsfiddle.net/5ExKF/3/

answered Dec 17, 2012 at 10:49

bipen

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