Javascript 2D array

Question

I am trying to use 2 dimensional array in javascript for storing strings. But I am not able to get the values correctly. Below is my code.

      var commentstore=new Array();
        function creating(id,day)
        {
            if(commentstore[day,id] != null)
         {
             alert("It already exists: commentstore["+day+"]["+id+"]"+commentstore[day,id] );
             var textinput="<div id='closeit'>Comments:<input type='text' name='comm["+day+"]  ["+id+"]' value='"+commentstore[day,id]+"'/></div>
                               <div id='closing' onclick='closecomment("+id+","+day+")'>:)</div>";
         }
            else
            {
                var textinput="<div id='closeit'>Comments:<input type='text' name='comm["+day+"]  ["+id+"]' /></div>
                               <div id='closing' onclick='closecomment("+id+","+day+")'>:)</div>";  
                $('#comm').html(textinput);
            }

    function closecomment(id,day)
    {
        comm.style.visibility='hidden';
        var str='comm['+day+']['+id+']';
        var element = document.getElementById(str);
     if(element.value !=null)
     {
      commentstore[day,id]=element.value;
      alert('New values stored: commentstore['+day+']['+id+']'+commentstore[day,id]);
     }
    }

So in the above code if commentstore[0,0]='man' then commentstore[1,0] and [2,0] and [3,0] ....[7,0] are also filled with 'man'. Same thing is happening with commentstore[0,1] even commentstore[4,1] scenarios. Can any one please provide any tutorial or sample code where we can dynamically create javascript 2d arrays. Thanks in advance.

Thank you all for helping. It is now working fine. I need to verify it more. Thanks again.. — Enjoy coding
– Enjoy coding, Commented Dec 28, 2009 at 15:58

Eli Acherkan · Accepted Answer · 2009-12-28 15:22:16Z

6

Replace commentstore[day,id] with commentstore[day][id]. That's the syntax for multi-dimensional arrays.

answered Dec 28, 2009 at 15:22

Eli Acherkan

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2 Comments

Enjoy coding Over a year ago

It is not working for me in the line if(commentstore[day,id] != null) . So I used ','. Is this because of IE.

Eli Acherkan Over a year ago

Please describe what isn't working, and whether you're getting any error messages.

Alsciende · Accepted Answer · 2009-12-29 08:53:51Z

1

Use commentstore[0][0] instead of commentstore[0,0]. Also, use strict comparaison whenever loose comparaison is not needed:

var commentstore = [];

function creating(id,day)
{
    if(commentstore[day] === undefined) commentstore[day] = [];
    if(commentstore[day][id] !== undefined)
    {
        alert("It already exists: commentstore["+day+"]["+id+"]"+commentstore[day][id] );
        var textinput="<div id='closeit'>Comments:<input type='text' name='comm["+day+"]  ["+id+"]' value='"+commentstore[day][id]+"'/></div>
                       <div id='closing' onclick='closecomment("+id+","+day+")'>:)</div>";
    }
    else
    {
        var textinput="<div id='closeit'>Comments:<input type='text' name='comm["+day+"]  ["+id+"]' /></div>
                       <div id='closing' onclick='closecomment("+id+","+day+")'>:)</div>";  
        $('#comm').html(textinput);
    }

function closecomment(id,day)
{
    comm.style.visibility='hidden';
    var element = document.getElementById(str);
    if(element.value !== '')
    {
        commentstore[day][id]=element.value;
        alert('New values stored: commentstore['+day+']['+id+']'+commentstore[day][id]);
    }
}

edit: in the original code, str is undefined and the execution fails. You can fix it in closecomment with:

var element = $('#closeit > input').eq(0);

edited Dec 29, 2009 at 8:53

answered Dec 28, 2009 at 15:23

Alsciende

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2 Comments

Enjoy coding Over a year ago

Thanks. This is giving error as object required at if(element.value) line. And alert is not coming in closecomment function

Alsciende Over a year ago

Indeed, str is undefined. You have to find the relevent input. Either by walking the DOM, or by identifying to input.

Aaron Digulla · Accepted Answer · 2009-12-28 15:31:40Z

-1

JavaScript only supports arrays with a single index but the index can be anything, so if you really want two dimensional arrays, do this:

commentstore[day+','+id] = ...

i.e. use a string with to components as the key.

answered Dec 28, 2009 at 15:31

Aaron Digulla

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4 Comments

Samir Talwar Over a year ago

Why on earth would you not use a proper multi-dimensional array? a = []; a[0] = []; a[0][1] = ...

Aaron Digulla Over a year ago

For example because of the initialization issue: You must create an array per index. With my solution, you can just assign anywhere. Also, my solution allows for arbitrary keys (not only integer) and sparse arrays. In a word, it's slower but generally more simple to use and understand and debug.

Alsciende Over a year ago

It's inefficient if you need to parse every record at a given index in the first dimension.

Aaron Digulla Over a year ago

@Alsciende: "inefficient"? Smells like premature optimization to me. With the new JIT compilers in the browsers, you won't notice a difference and it will make your code much more simple. What's worth more? 12ms in millions of browsers or a week of your time tracking down obscure bugs?

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