Adding dynamically to multidimensional array javascript?

Question

var oparea = [];
var mainarr_index = 0;

$("input.oparea-name").each(function(opera_key) {                                  
    var name_oparea = $(this);
    oparea[mainarr_index]['maincat']['name'] = name_oparea.val(); //Add to array

    $(subcats).each(function(index) { 
        oparea[mainarr_index]['subcat']['name'].push(name_subcat);
    }

    mainarr_index++;
}

The result I want:

oparea[0]['maincat']['name'] = 'name of oparea1';
oparea[0]['maincat']['subcat'] = array('name' => array('subcatname1', 'subcatname2'));

oparea[1]['maincat']['name'] = 'name of oparea2';
oparea[1]['maincat']['subcat'] = array('name' => array('subcatname1', 'subcatname2'));

//etc etc

The result I get in console is:

Uncaught TypeError: Cannot read property 'maincat' of undefined

Of course it's undefined, therefore I want to define it ;-)

How can I achieve what I want?

It's better to use push method instead direct element access — hindmost
– hindmost, Commented Jan 2, 2016 at 15:29
I don't understand how to achieve that . It's very important that key for opera['subcat'] and opera['maincat'] are equal. If I do a push on the maincat they won't be. — bestprogrammerintheworld
– bestprogrammerintheworld, Commented Jan 2, 2016 at 15:32

bestprogrammerintheworld · Accepted Answer · 2016-01-02 15:49:09Z

2

You can't set the property of an object if there's no object there to begin with. And you can't push onto an array if the array hasn't been created yet (I suspect you're used to PHP, which will fill these things in automatically when necessary).

And you can use .push to add the new object to the array, instead of using the oparea_index variable.

$("input.oparea-name").each(function(opera_key) {                                  
    var name_oparea = $(this);
    var new_oparea = {
        maincat: {
            name: name_oparea.val()
        },
        subcat: {
            name: []
        }
    };

    $(subcats).each(function(index) { 
        new_oparea.subcat.name.push(name_subcat);
    }

    oparea.push(new_oparea);
}

edited Jan 2, 2016 at 15:49

bestprogrammerintheworld

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answered Jan 2, 2016 at 15:32

Barmar

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4 Comments

bestprogrammerintheworld Over a year ago

Aha. Thanks a lot! And yes, you're susipicion about PHP was correct :-)

Barmar Over a year ago

FYI, if you turn on warnings in PHP, it will complain about code like that.

Barmar Over a year ago

Where does name_subcat come from?

bestprogrammerintheworld Over a year ago

name_subcat is supposed to be given by dynamically created input elements under the opareas. I could not paste in the whole code here though :-)

Duang · Accepted Answer · 2016-01-02 15:46:30Z

1

var oparea = [];
$("input.oparea-name").each(function(opera_key) {                                  
    var name_oparea = $(this);
    if(!oparea[mainarr_index]){
        oparea[mainarr_index]={};
    }
    if(!oparea[mainarr_index]['maincat']){
        oparea[mainarr_index]['maincat']={};
    }
    oparea[mainarr_index]['maincat']['name'] = name_oparea.val(); //Add to array

    $(subcats).each(function(index) { 
        if(!oparea[mainarr_index]){
            oparea[mainarr_index]={};
        }
        if(!oparea[mainarr_index]['subcat']){
            oparea[mainarr_index]['subcat']={};
        }
        if(!oparea[mainarr_index]['subcat']['name']){
            oparea[mainarr_index]['subcat']['name']=[];
        }
        oparea[mainarr_index]['subcat']['name'].push(name_subcat);
    }
}

answered Jan 2, 2016 at 15:46

Duang

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1 Comment

bestprogrammerintheworld Over a year ago

I guess this would work also, but I think Barmars solution is "cleaner" (eaiser to read and understand the code).

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