How to select an object inside array that has a specific value in JS

Question

How do I select an object inside an array where the object has the the value "A" for the "slug" key?

for example if I have this:

 var allItems = [
    {
        "slug": "henk",
        "company_founded": "2008",
        "company_category": "Clean",
        "company_logo": false,
        "company_description": "",
    }
    {
        "id": "bas",
        "company_founded": "2012",
        "company_category": "Health",
        "company_logo": false,
        "company_description": "",
    }
    {
        "slug": "jan",
        "company_founded": "2005",
        "company_category": "Clean",
        "company_logo": false,
        "company_description": "",
    }
]

What I want is to put the object that contains the slug : henk inside a new variable.

So I will have something like this to work with:

var = SelectedItem = {
    "slug": "henk",
    "company_founded": "2012",
    "company_category": "Health",
    "company_logo": false,
    "company_description": "",
}

Thanks!

if you want the henk subobject, why are you saying you need to get the bas one out of it? — Marc B
– Marc B, Commented Jan 28, 2016 at 21:06
please state, what you are looking for, what value what key have and why the result is with henk and 2012? — Nina Scholz
– Nina Scholz, Commented Jan 28, 2016 at 21:09
IF you had a consistent set of elements you could create a lookup but there is no consistency so you have to iterate the list for the specific instance. — Mark Schultheiss
– Mark Schultheiss, Commented Jan 28, 2016 at 21:12
I was looking for a way to select the object that contains henk. But it's solved thanks! — Raymond the Developer
– Raymond the Developer, Commented Jan 28, 2016 at 21:13

Stefan Falk · Accepted Answer · 2016-01-28 21:07:15Z

1

You will have to iterate your list and based on your condition take the element that you are looking for:

var result;
for each (var item in allItems ) {
    if(item.company_founded === "2012") {
        result = item; 
        break;
    }
}

answered Jan 28, 2016 at 21:07

Stefan Falk

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2 Comments

Raymond the Developer Over a year ago

Omg so obvious. Thanks!

Stefan Falk Over a year ago

@RaymondtheDeveloper You are welcome. However, if you have a lot of data and need to look up items very often from such a list/set then you might want to consider converting your list into a dictionary. This would allow you to access an item much faster through one particular identifier. This is what Fire Crow suggested. Of course you don't need that if you have to do that only once, or let's say, not that often that it would have bad impact on actual performance.

MinusFour · Accepted Answer · 2016-01-28 21:19:09Z

1

You might want to look up into Array.prototype.find:

 var obj = allItems.find(function(el){
     return el.slug === 'henk';
 });

answered Jan 28, 2016 at 21:19

MinusFour

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Comments

Nina Scholz · Accepted Answer · 2016-01-28 21:20:55Z

For mixed up object, you can iterate over all properties and return only the object which some propertiy has a certain value.

var allItems = [{ "slug": "henk", "company_founded": "2008", "company_category": "Clean", "company_logo": false, "company_description": "", }, { "id": "bas", "company_founded": "2012", "company_category": "Health", "company_logo": false, "company_description": "", }, { "slug": "jan", "company_founded": "2005", "company_category": "Clean", "company_logo": false, "company_description": "", }],
    result = allItems.filter(function (a) {
        return Object.keys(a).some(function (k) {
            return a[k] === 'henk';
        });
    });

document.write('<pre>' + JSON.stringify(result, 0, 4) + '</pre>');

Mark Schultheiss · Accepted Answer · 2016-01-28 21:49:19Z

Make it consistent: Array of objects (put comma between, changed id to slug to match others.)

Assumption is that the property is unique OR it will get the LAST ONE in the list. Like an ID lookup or some such.

EDITED to show value within complex object vs simple array EDIT2: add second lookup by category

var allItems = {"fred":"H fred",rats:"rats",lookupitems: [{
  "slug": "henk",
  "company_founded": "2008",
  "company_category": "Clean",
  "company_logo": false,
  "company_description": "",
} ,{
  "slug": "bas",
  "company_founded": "2012",
  "company_category": "Health",
  "company_logo": false,
  "company_description": "",
}, {
  "slug": "jan",
  "company_founded": "2005",
  "company_category": "Clean",
  "company_logo": false,
  "company_description": "",
}]};

Create a lookup we can use in a repeatable fashion:

var lookup = {};
var lookupbycategory = {};
// create reference to list above and use it everywhere
lookup.list = allItems.lookupitems;
for (var i = 0, len = lookup.list.length; i < len; i++) {
  lookup[lookup.list[i].slug] = lookup.list[i];
  lookupbycategory[lookup.list[i].company_category] = lookup.list[i];
}

Get one (use it)

var mychoice = lookup["henk"];
alert(JSON.stringify(mychoice));
alert(JSON.stringify(lookupbycategory["Clean"]));

reuse it

var mybas = lookup["bas"];

Fire Crow · Accepted Answer · 2016-01-28 22:20:54Z

1

You may consider storing the values in an object indexed by the expected keys, such as:

var allItems = {
  "henk":
    {
        "slug": henk,
        "company_founded": "2008",
        "company_category": "Clean",
        "company_logo": false,
        "company_description": "",
    },
  "bas":
    {
        "id": bas,
        "company_founded": "2012",
        "company_category": "Health",
        "company_logo": false,
        "company_description": "",
    }
]

this allows you to retrieve a value like allItems.henk

it indexes faster because it's a logarithmic hash-table look up instead of a full iteration.

----- edit ----

if you need to transform it in advance to accelerate lookup, as long as the cost of generating the new structure is less than the cost of the lookups you will be doing. you can do,

var allItemsByKey = {}
for(var i = 0, l = allItems.length; i<l; i++){
   var item = allItems[i];
   allItemsByKey[item.slug] = item;
}

then allItemsByKey has the structure demonstrated above

edited Jan 28, 2016 at 22:20

answered Jan 28, 2016 at 21:17

Fire Crow

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2 Comments

Raymond the Developer Over a year ago

Ah yes this is indeed the best way to store values. But it's generated by an external party where I have no control of. I'll use this way for my own when I need to. Thanks!

Fire Crow Over a year ago

a transformation may not be inefficient depending on the problem space, I'll amend the response

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